• Magnetic field direction is N to S outside the magnet.
• Magnetic field direction is S to N inside the magnet.
• Magnetic field lines representing the strength and direction of the magnetic field.
• Magnetic field lines are continuous lines, forming closed loops.
  
  

• Fe, Co, Ni. (they are called ferromagnetic)

• Heating
• Magnetism

• When charge moves in a medium, it generates a magnetic field perpendicularly around that medium.
• This is electromagnetism (Below is an electromagnet).

Total magnetic flux depends on:

• Strength of the field

• Size of the surface it passes through

• Orientation of the surface

For a loop of area (A) in the presence of a uniform magnetic flux density (B), the magnetic flux (Ф) passing through the loop is:

• Ф = BA cos θ

  • where θ = angle between magnetic flux density (B) and the normal to the loop of area (A).

  • where B = the magnetic field strength (in Tesla)

  • where A = area of the coil loop

  • Unit for Ф = Wb (Weber)

• Faraday's Law = The emf induced in a coil/conductor is directly proportional to the rate of change of magnetic flux linkage.

• Flux linkage = The product of the number of turns on the coil and the flux through the coil (NФ)

• Number of turns in the coil
• Rate of change of flux 

• the position of the NORMAL TO THE COIL relative to the magnetic field relates to the flux linkage magnitude.

• The emf induced in the coil acts to oppose any change in the magnetic flux.
• Work is done to push the permanent magnet against the coil's induced magnetic field.
• Energy is conserved (E_mechanical --> E_electrical).

• gives the direction of an induced EMF which induces a current flow. 
• the current flows in a direction to oppose the change (an increasing or decreasing magnetic field) causing it.

• A current is passed through a coil in a magnetic field, causing a force and the coil MOVES. A motor works on the principle of the motor effect.

• A coil is rotated through a magnetic field, CAUSING A CURRENT to flow in the coil as the wire cuts across the magnetic field. This causes a changing magnetic field. 
• A generator works on the principle of electromagnetic induction.
• Induction = the production of current in a conductor as it moves through a changing magnetic field.
• Faraday's Law of Induction applies in generators, stating that:
• if a wire is moved back and forth in a magnetic field, it cuts across the lines of magnetic flux. This magnetic field pushes on electrons in the metal. This movement of electrons is electrical flow.

• "B" - Strength of the magnetic field (flux density of the magnet)
• "I"  - Current flowing or generated in the coil
• "ℓ" - Length of the conductor in the magnetic field
• "θ" - Angle between the conductor and the fixed magnetic field
• Use this formula for calculations: 
  • F = B x I x ℓ x sin θ    
  • Also: F = Bqv ; q=charge, v=speed of rotor

• Position of the coil
  • If parallel to the external magnetic field (B), then flux lines are not 'cut' and zero induced emf is generated.
  • If perpendicular to an external magnetic field (B), then flux lines are being 'cut' and an induced emf is generated.
• Strength of the magnetic field
• Number of turns on the coil
• Area of the coil
• Coil wound around an iron core or not.
• Rotation speed of the coil 
  • i.e. Rate of change in magnetic flux or rate with which coil "cuts" across the permanent magnetic field

• The Number of turns on the primary and secondary coils affect the input and output voltages.

• Our household power is generated as AC in power stations.
• Most devices is not compatible with AC, but uses DC to operate. 

• Like a sort of water VALVE. 
• Signal diodes
• Rectifier diodes

• Check if the quantity’s effect depends on its square (use RMS) or linear value (use average).

• For oscillatory systems or energy-related calculations, use RMS; for straightforward averages, use arithmetic mean.

• Check if the quantity’s effect depends on its square (use RMS) or linear value (use average).

• For oscillatory systems or energy-related calculations, use RMS; for straightforward averages, use arithmetic mean.

• Check if the quantity’s effect depends on its square (use RMS) or linear value (use average).

• For oscillatory systems or energy-related calculations, use RMS; for straightforward averages, use arithmetic mean.

a) Define the term Root Mean Square (RMS) voltage and explain why it is used instead of the arithmetic average for AC circuits. (3 marks)

b) Calculate the RMS voltage of the household supply. Show all working and round your answer to two decimal places. (3 marks)

c) Calculate the average power dissipated by the resistive appliance when connected to this AC supply. Show all working and round your answer to the nearest watt. (4 marks)

d) Explain how the RMS voltage relates to the power generated by the appliance, and why it is critical for determining the correct power rating of electrical devices in a household. (3 marks)

Total: 13 marks

Marking Guidelines

• a) Definition:

  RMS voltage is the square root of the mean of the squared voltages over one cycle, representing the equivalent DC voltage that produces the same power. (1)
  

• Explanation: The arithmetic average of AC voltage is zero due to alternating positive and negative values, making it unsuitable for power calculations, whereas RMS accounts for the effective power delivered. (2)