ELECTRICITY - GR11 BISHOPS by Lizelle Swanepoel https://padlet.com/lizellexs/blrigdidmjw27rr en-us 2021-10-10 21:38:51 UTC 2025-10-27 06:36:22 UTC hello@padlet.com https://padlet.net/icons/png/1f4a1.png ELECTRIC CIRCUITS - Matric Finals Paper 1 weighting lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117810 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117810 FORMULAE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117812 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117812 What is electricity? lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117814 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117814 THREE BASIC ELECTRICAL QUANTITIES: I, V, R lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117815 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117815 SERIES VS. PARALLEL CIRCUITS RULES SUMMARY lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117816 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117816 CONSTRUCT YOUR OWN CIRCUITS lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117817 PHET]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117817 CURRENT = The rate of flow of charge between two points in a circuit lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117818 Current = The rate of flow of charge between two points in a circuit. ]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117818 CURRENT FLOW IN METALS lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117819 Metals consist of positive ions surrounded by a “sea” of delocalised electrons. 
  • The delocalised electrons are free to move through the crystal structure. 
  • When connected to a power source, the electrons all drift in the same direction which creates an electric current (flow of charge at a certain rate).
]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117819 VOLTAGE = Electrical energy transferred per unit positive charge between two points in a circuit lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117820
Voltage = Electrical energy transferred per unit positive charge between two points in a circuit.
OR Work done per unit positive charge.
EMF = The maximum energy provided by a battery per unit charge passing through it.

In Layman's terms we could say:
VOLTAGE = The "PUSH" behind the charge in the circuit.

]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117820 WHICH EQUATION TO USE? lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117821 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117821 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117822 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117822 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117823 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117823 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117824 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117824 Ammeters and Voltmeters lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117826 An ammeter measures current in a circuit. 
  • An ammeter has VERY LITTLE RESISTANCE. 
  • An ammeter is always connected in SERIES with components in a circuit, as it must allow all the current to flow through it in order to measure current. 

A Voltmeter measures potential difference between two points in a circuit. 
  • A voltmeter has GREAT RESISTANCE. 
  • A Voltemeter must therefore always be connected in parallel with a component in a circuit, in order to measure the difference in potential energy between two points right before and after a resistor. 

]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117826 RESISTANCE = A material’s opposition to the flow of current through it and is the ratio of potential difference across the ends of a conductor and current strength. lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117827 Resistance = A material’s opposition to the flow of current through it.

The factors that affect resistance of a resistor: 
  • Length
  • Thickness
  • Temperature
  • Type of material (resistivity)

State the relationship between resistance and each of these factors, and give a reason for each relationship. 
]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117827 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117828 3. Potentiometer (another type of variable resistor)]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117828 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117829 2. Variable resistor (rheostat)]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117829 RESISTORS - DIFFERENT TYPES lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117830 1. Fixed resistors]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117830 RESISTOR SYMBOLS lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117831 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117831 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117833 Thor's magical weapon]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117833 WORKED EXAMPLE - TOTAL RESISTANCE: SERIES VS PARALLEL lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117836 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117836 THEORY RECAP lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117837 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117837 CELLS IN SERIES VS PARALLEL lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117838 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117838 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117839 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117839 DEFINITIONS lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117840 ·       CURRENT (I=Q/t)
The rate of flow of charge between two points in a circuit.
 
·       POTENTIAL DIFFERENCE (V=W/q)
The work done per unit positive charge 
 
·       EMF
The maximum energy provided by a battery per unit charge passing through it. 
 
·       RESISTANCE (R=V/I)
A material's opposition to the flow of electric current, and it is the ratio of potential difference across the ends of a conductor and current strength.
 
·       OHM’S LAW (R =V/I)
The potential difference across a conductor is directly proportional to the current in the conductor at constant temperature. 
 
·       KILOWATT HOUR (kWh=P.t)
The kilowatt hour (kWh) is a unit of energy and 1 kWh is the amount of energy used when 1 kilowatt of electricity is used for 1 hour.
 
·       INTERNAL RESISTANCE (Emf=IR+Ir)
The resistance inside a real battery. 
]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117840 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117842 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117842 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117844 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117844 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117845 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117845 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117846 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117846 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117847 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117847 RELATIONSHIP BETWEEN I, V and R - OHM'S LAW lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117848 Current through a conductor is directly proportional to potential difference across a conductor, provided the temperature of the conductor stays constant.
Therefore:
R = V/I ]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117848 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117849 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117849 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117850 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117850 OHM'S LAW EXPLAINED lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117851 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117851 VERIFYING OHM'S LAW lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117853 EXPERIMENT]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117853 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117854 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117854 EXAMPLE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117858 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117858 EXAMPLE SOLUTIONS lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117860 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117860 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117861 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117861 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117862 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117862 Voltage drop across a resistor lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117863 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117863 RESISTORS ADDED INTO A CIRCUIT lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117864
  • When resistors are added in series, the total resistance increases. 
  • When resistors are added in parallel, the total resistance decreases.
  • When a load is connected to a battery, the voltmeter connected across the battery will be the reading for 𝑉 𝑒𝑥𝑡.

    • ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117864     CHECK POINT lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117866 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117866 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117867 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117867 DO THIS PROBLEM lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117868 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117868 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117869 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117869 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117871 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117871 EXAM STYLE QUESTION lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117872 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117872 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117873 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117873 HOW TO ANALYSE A CIRCUIT USING THE COLOUR CODING TECHNIQUE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117876 Red = High electrical potential
    Blue = Low electrical potential]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117876     R4 is shorted out the circuit. No current passes through R4. lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117877 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117877 TRY THIS CIRCUIT lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117878 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117878 ELECTRIC POTENTIAL COLOUR CODING TECHNIQUE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117881 Watch this video:]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117881 Electrical lighting facts about the Eiffel Tower lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117883
  • Number of lightbulbs = 20 000
  • Power of each bulb = 6 W
  • Length of cabling = 40 km
  • The Eiffel starts twinkling at 10 pm to 1 am every day.
    • ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117883     lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117884 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117884 CIRCUIT PROBLEMS - WORKED EXAMPLE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117886 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117886 POWER lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117887 James Watt invented the steam engine and coined the unit for power as the Watt. ]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117887 ELECTRICAL ENERGY lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117888 Thomas Edison commercialized electricity, which we still pay for today, per kiloWatt-hour (kWh). ]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117888 JOSEPH SWAN lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117889 Inventor of the first carbon filament evacuated light bulb - one year before Edison. ]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117889 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117890 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117890 COMMERCIALIZING ELECTRICITY lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117891 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117891 WATCH THIS VIDEO lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117893 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117893 ENERGY vs. POWER lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117894 Energy = the ability to do work.
    Power = the rate at which work is done/the rate at which electrical
    Energy is transferred between two points in a circuit. 

    ENERGY IN A CIRCUIT
    • A cell forces charge to move in a complete circuit. 
    • The charge is supplied with electrical energy in the cell as a result of chemical reactions that take place inside the cell. 
    • As the charge passes through each component in the circuit, work (W) is done by the cell to drive charge through the component
    • Electrical energy is converted into other forms of energy in circuit elements.
    • We say that electrical energy is dissipated in a resistor (converted to other energy forms).
    • E = W
      • The work done (W) in moving the electric charge between the ends of a resistor is equal to the energy dissipated in the resistor. 
      • The symbol for electrical energy will also be W.
      • It is measured in Joules (J) as the unit.
    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117894     HEATERS CONVERT ELECTRICAL ENERGY INTO HEAT ENERGY lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117895 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117895 INCANDESCENT LIGHTBULB FILAMENT lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117896 It converts electrical energy into heat energy]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117896 TOASTERS CONVERT ELECTRICAL ENERGY INTO HEAT ENERGY lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117897 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117897 ELECTRICAL ENERGY DISSIPATED IN A CIRCUIT ELEMENT (RESISTOR) lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117898 Deriving three equations for electrical energy from fundamental principles:]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117898 CHECK POINT ON ELECTRICAL ENERGY lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117899
    A torch bulb uses two 1,5 V cells connected in series. The bulb has a resistance of 16,3 Ω.

    a) Calculate the electrical energy dissipated in the torch bulb in 5 minutes.



    b) Calculate the current in the torch bulb.



    c) Suppose the same bulb is connected to another battery (for the same length of time) so that the current in the torch bulb is doubled. By what factor would the amount of electrical energy dissipated in the bulb change?



    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117899     POWER DISSIPATED IN A RESISTOR/DELIVERED BY A BATTERY lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117900 Derive these formulae]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117900 POWER RATINGS lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117902 The power value written on any device is the rate at which it can convert electrical energy into other forms of energy. 
    A value of say 20W means that 20J of energy is converted per second. ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117902     BRIGHTNESS OF A BULB DEPENDS ON THE POWER DELIVERED TO IT lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117903 Explain this:]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117903 POWER - WORKED EXAMPLE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117904 An electric kettle is rated at 2,2 kW, 240 V. The supply voltage is reduced from 240V to 230V. Calculate the new power of the kettle.













    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117904     COST OF ELECTRICITY USAGE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117905 Electrical energy consumed is measured in kilowatt hours (kWh). 
    • 1 kWh refers to the use of 1 kW of electricity for 1 hour.
    • 1 kWh is equivalent to 3 600 000 J of electrical energy:
    • 1 kWh = 1 000 W × 1 h = 1 000 W × 3 600 s = 3 600 000 J

    Electrical consumption is charged per kWh used.

    EXAMPLE 1:
    Suppose a 1100 W electrical iron is used for 4 hours and the cost of electrical energy is 61c per kWh. What is the cost of using the iron for 4 hours?

    Cost = Power rating of appliance (in kW) × time used (in hours) × price per kWh

             = 1,1 kW × 4 hours × 61c = 268,4c = R 2,68


    EXAMPLE 2: 
     An electric kettle has a power output of 2,2 kW 240 V. 
     
    a) Calculate the current in the kettle.
     




    b) Calculate the resistance of the kettle element. 
     




    c) Calculate the cost of using the kettle for 5 hours if the cost per kWh is 61c.





    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117905     INTERNAL RESISTANCE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117908 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117908 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117909 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117909 INTERNAL RESISTANCE INSIDE A BATTERY lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117910 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117910 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117911 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117911 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117912 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117912 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117913 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117913 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117914 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117914 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117915 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117915 CHECKPOINT 14 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117916 A cell of unknown emf and internal resistance is connected in series with a 16 Ω resistor and a voltmeter connected across the resistor reads 1,2 V. When the 16 Ω resistor is replaced with an 8Ω resistor, the voltmeter reads 1 V.

    a) Draw a neat circuit diagram and explain why the voltmeter reading decreased when the resistance was decreased.

    b) Calculate the emf and internal resistance of the cell.

    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117916     lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117917 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117917 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117918 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117918 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117919 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117919 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117920 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117920 INTERNAL RESISTANCE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117921 Watch this video.]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117921 INTERNAL RESISTANCE PRAC lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117922 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117922 To determine the internal resistance of a battery of cells: lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117923 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117923 Consider the equation below: lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117924   
    Rearrange the equation into the form of a straight line graph  to match the quantities plotted on the graph. 
    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117924     Rearranged into y = mx + c form: lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117926 Emf   =  Vext  +  Ir
    Vext  =  -rI      +  Emf
       (y  =   mx    +    c)

    Where:   y-int  =  Emf
                        m  =  - r
                        x   =  I

    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117926     What is the maximum current which can be delivered by the battery? lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117927
  • For max current (off the graph), Vext = 0.
  • Hence:     
    •                          Vext  =  -rI      +  Emf
                                  0  =  -rI      +  Emf
                             Emf  =  rI
                                   I  =  Emf / r 
                                      =  y-int / gradient

    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117927     SUMMARY lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117928 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117928 WITH INTERNAL RESISTANCE IN THE BATTERY: lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117929
  • If more resistors are added in series:
    • 1. The total resistance (𝑅T ) increases.
    2. The current in the main circuit will decrease, since the emf of the battery remains constant. (I ∝ 1/R)
    3. Vlost  will decrease, since the internal resistance remains constant. (Vlost = Ir)
      4. Vext  will increase, since the emf remains constant. (by Emf = Vext + Vlost)

    • If more resistors are added in parallel:
    1. Total resistance decreases. 
    2. Current in mains and through the battery increases. 
    3. V lost increases. (Vlost = Ir)
    4. Vext will decrease since emf stays constant. (by Emf = Vext + Vlost)

    • Graphs:
    In the graph of Vext (measured across battery) vs 𝐼 (measured in a series part of the external main circuit), the emf of the battery is given by the y-intercept (when the load current is 0 A).
    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117929     SUMMARY ON INTERNAL RESISTANCE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117930 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117930 MATRIC PORTFOLIO PRAC - DETERMINING THE INTERNAL RESISTANCE OF A BATTERY: lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117932 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117932 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117933 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117933 PRACTICAL - MEASURING INTERNAL RESISTANCE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117934 NOTE:
    • EMF = Voltage across battery when the circuit is open (I=0).
    • Terminal PD = Voltage across battery when charge is flowing through it.
    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117934     EXAM QUESTION - INTERNAL RESISTANCE lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117935 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117935 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117937 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117937 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117938 They repeat the above steps for different sliding contact positions and tabulate the readings:]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117938 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117939 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117939 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117940 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117940 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117942 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117942 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117943 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117943 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117944 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117944 How can a graph of data be more informative than a table of the same data? lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117945
  • A graph provides a visual informational view instead of simply numbers on a table.
  • Some of the numbers may be anomalies, and using them in a formula will increase the percent error from the accepted value.
  • The more data collected, the more points can be plotted on the graph for a more accurate line of best fit.
  • It presents a more accurate value of the metric you want to calculate.
    • ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117945     WHAT IS "AMP-HOURS"? lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117946 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117946 WATT-HOURS lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117947 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117947 SUMMARY OF VOLTAGE, CURRENT, AC VS DC, POWER, WATT-HOURS, CALCULATING WATT-HOUR RATING OF A BATTERY, PARALLEL-SERIES CONNECTIONS lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117948 This video is brilliant - make sure to watch it!]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117948 YOUR "I CAN" LIST lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117951 This is your I CAN list to reflect on your learning on this section:
    • Check each point on the white list below and make sure you can do each. 
    • If you are still unsure of a sub-section, establish your mastery doing the following:
      • revisit that section in the Notes
      • re-watch my posted teaching Videos on Classroom and YouTube
      • do Past Papers
    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117951     GENERAL MISCONCEPTIONS ABOUT SIMPLE CIRCUITS lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117953 Students sometimes fail to discriminate between these terms and concepts:
    • Potential difference:
      • emphasizes that we are measuring a change in “push” between two different points in an electric circuit.
    • Electromotive force (emf):
      • a term for 'voltages' across sources of electrical energy.
    • Cells becoming 'discharged' 
      • charge is not used up, energy is transferred.
    • Conventional current: 
      • This flows (by definition) from positive to negative around the external circuit 
      • Inside the cell chemical reactions ‘pump’ charge carriers to the terminals. 
      • Some may say that ‘physicists got it wrong because we now know that electrons flow the other way.’ 
      • But it is really an arbitrary choice. 
      • One can illustrate this by looking at current flow and movement of charge carriers in an electrolyte (or an ionized gas). 
      • Positive ions go one way, negative ions go the other way. 
      • And so, however current is defined, there are always examples where current direction and charge carrier movement are opposite.

    • Current flows all around a circuit:
      • including through the cell itself.

    • Analogy for charge flow is a bicycle Chain:
      • This transfers energy from you (equivalent to the cell) to the rear wheel. 
      • The chain is not used up (neither is charge), 
      • and does not disappear when you run out of energy (when the cell runs flat and the chemical reactions within it stop).
      • It has no beginning and no end. 
      • It moves as a SYSTEM, every part all at once. 
      • this is the CYCLIC SIMULTANEOUS MODEL OF ELECTRIC CIRCUITS. 

    • Another analogy:
      • Skiers (charges) being lifted up a mountain by a ski lift (external energy source/emf/cell) and then skiing down a slope (resistor). 
      • This is useful for the idea of voltages in parallel circuits. 
      • Parallel slopes drop different skiers through the same vertical height (equal voltages across components in parallel).
    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117953     PAST PAPERS (2015-2019) lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117955 (Open this doc on iPad or laptop)]]> 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117955 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117956 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117956 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117957 2015 SUP

    ]]>     2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117957     NOTES 2023 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117958 2021-10-10 21:38:51 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806117958 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806130224 2021-10-10 21:50:13 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1806130224 INTERNAL RESISTANCE PRAC lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1858857729 2021-11-01 14:06:49 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/1858857729 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/2334187033 Thor's magical weapon]]> 2022-10-10 20:47:34 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/2334187033 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/2334218655 2022-10-10 21:29:35 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/2334218655 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/2334236451 2022-10-10 21:56:42 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/2334236451 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/2334242313 2022-10-10 22:04:11 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/2334242313 EXAM STYLE QUESTION lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/2750164755 2023-10-17 05:57:11 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/2750164755 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/3647288016 2025-10-23 11:44:50 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/3647288016 lizellexs https://padlet.com/lizellexs/blrigdidmjw27rr/wish/3647288242 2025-10-23 11:45:02 UTC https://padlet.com/lizellexs/blrigdidmjw27rr/wish/3647288242