GR10 ELECTRICITY by Lizelle Swanepoel

CHARGE: Q = It

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Q=It

HOW BATTERIES PROVIDE ELECTRICAL ENERGY IN ELECTRICAL CIRCUITS

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What is electricity?

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CURRENT FLOW IN METALS

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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).

Ammeters and Voltmeters

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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.

V,I,R SUMMARY - SERIES VS PARALLEL CIRCUITS

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CURRENT

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Current strength = The rate of flow of charge between two points in a circuit.
I = Q/t

VOLTAGE

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Voltage = Electrical energy required to transfer a unit charge between two points in a circuit.

Voltage = The electrical energy required to move one coulomb of charge between two points.

VOLTAGE = The "PUSH" behind the charge in the circuit.
EMF = The quantity of electrical energy that can be supplied per coulomb of charge when no current is flowing through a cell.

RESISTANCE

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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.

RELATIONSHIP BETWEEN I, V and R

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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

OHM'S LAW

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Solving circuit problems using Ohm’s Law (R=V/I)

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CIRCUIT PROBLEM

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VERIFYING OHM'S LAW

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EXPERIMENT

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HOW TO CALCULATE TOTAL RESISTANCE IN SERIES VS PARALLEL

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TYPICAL CIRCUIT QUESTION

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RESISTORS - DIFFERENT TYPES

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1. Fixed resistors

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2. Variable resistor (rheostat)

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3. Potentiometer (another type of variable resistor)

CHECK POINT 5

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CHECK POINT 6

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CHECKPOINT 7

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EXAMPLES

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RESISTORS IN SERIES VS PARALLEL - RULES

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SERIES-PARALLEL COMBINATION (COMPLEX) CIRCUITS

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Calculations:

Answer these questions:

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(a) Calculate the total resistance in the circuit.
(b) Calculate the readings on voltmeters V1 and V2.
(c) Calculate the current in the 2 Ω resistor.
(d) How would the reading on the ammeter change if:
(i) Switch S was opened? Explain your answer.
(ii) Switch S is closed and the 5 Ω resistor is removed from the circuit. Explain
your answer.

Solution:

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HOMEWORK FOR NEXT LESSON

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SERIES-PARALLEL CIRCUITS

LET'S MARK!

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EXERCISE 2 - CONTINUED

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FURTHER CIRCUIT PROBLEMS - HOW TO SOLVE

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DECREASING THE TEMPERATURE OF A RESISTOR

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WHAT IS THE EFFECT OF TEMPERATURE ON RESISTANCE?

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Here temperature in increased. Watch how resistance is increased:

WHAT IS RESISTANCE?

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WHAT IS THE EFFECT OF TEMPERATURE ON THE RESISTANCE OF A RESISTOR?

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YOUR TASK FOR TODAY: BUILD A FOIL CIRCUIT

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What’s great about electricity and circuits is that you can make one at home without any special equipment.
And there’s something really cool about being allowed to freely explore with wires and batteries!

MATERIALS YOU WILL NEED, METHOD, QUESTIONS & HOMEWORK

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aluminum foil (known as "foil" from the grocery store)
adhesive tape (like sellotape)
an A4 piece of paper (or anything bigger is also fine)
3 torch batteries or three 3 Volt coin batteries
paper clips
3 small light bulb (an LED or one from a flashlight)

How to Make a Simple Circuit - follow these steps:
Step 1: Cut two pieces of foil and fold into strips (acting as wires for the circuit).
Step 2: Tape one foil piece to the + end of one battery & the other to the - end.
Step 3: Touch one strip to the metal part of the bulb, just under the glass.
Step 4: Touch the other strip to the silver tip on the end of the bulb. Use a paper clip to make connection between the battery and foil if using a 3 V coin battery.
Step 5: Save your video onto your YouTube channel.
Step 6: Post the link to Classroom for HOMEWORK.

Answer these questions:
1. What happens when you add two or more batteries to your circuit? Compare.
2. Build a series circuit with 2 or 3 light bulbs. Take a video of how it works.
3. Build a parallel circuit with 2 or 3 light bulbs. Take a video of how it works.
4. What do you observe about the difference between the brightness of your light bulbs in the series vs parallel circuit?
5. Build something functional and cool with your circuit.
6. Take a video of how your circuit works performing its function.
7. Save your video onto your YouTube channel.
8. Post the link to Classroom for HOMEWORK.

This activity will challenge you to explore.
Have fun and make this section on electrical circuits "light up" for you!

Voltage drop across a resistor

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FURTHER WORKED PROBLEMS

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HEREWITH SOME HANDS-ON PAPER-FOIL CIRCUITS!

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EXAM STYLE QUESTIONS

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MEMO

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THEORY RECAP

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TASK

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BUILD YOUR OWN CIRCUIT - PhET SIM

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NOTES - BISHOPS

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THREE MAIN COMPONENTS OF A CIRCUIT

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FILL IN THE TABLE

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WHAT YOU SHOULD BE ABLE TO DO BY THE END OF THIS UNIT

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Tick off what you can do as we progress through the unit):
• Define and calculate current in a circuit.
• Define the SI unit of charge: the coulomb.
• Describe the conditions necessary for charge to flow.
• Define and calculate electrical potential difference (voltage in a circuit).
• Define the volt.
• Differentiate between the emf of a cell and the potential difference across
components in a circuit and calculate resistance;
• Define the SI unit of resistance: the ohm.
• Describe how to measure voltage, current and resistance using the
appropriate instruments.
• Compare the effective resistance of series vs. parallel circuits.
• Calculate the effective resistance of resistors in series and in parallel, and
series-parallel combinations of resistors.

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THREE PARAMETERS IN ELECTRICITY

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ELECTRICAL ENERGY

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Thomas Edison commercialized electricity, which we still pay for today, per kiloWatt-hour (kWh).

JOSEPH SWAN

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Inventor of the first carbon filament evacuated light bulb - one year before Edison.

COMMERCIALIZING ELECTRICITY

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COST OF ELECTRICITY USAGE

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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.