25.3 The AC current generator

The direction of the induced current in the coil of a generator depends on the …

• length of the coil.

• speed of rotation of the coil.

• direction of the magnetic field.

• strength of the magnetic field.

Which ONE of the following combinations regarding the energy conversions in electric motors and electric generators is CORRECT?

• ENERGY CONVERSION IN MOTORS: Mechanical to electrical

  ENERGY CONVERSION IN GENERATORS: Electrical to mechanical

• ENERGY CONVERSION IN MOTORS: Mechanical to electrical

  ENERGY CONVERSION IN GENERATORS: Mechanical to electrical

• ENERGY CONVERSION IN MOTORS: Electrical to mechanical

  ENERGY CONVERSION IN GENERATORS: Electrical to mechanical

• ENERGY CONVERSION IN MOTORS: Electrical to mechanical

  ENERGY CONVERSION IN GENERATORS: Mechanical to electrical

Which ONE of the following actions will NOT cause an increase in the induced emf in a coil if the coil is rotated in a uniform magnetic field?

• Rotating the coil faster

• Increasing the strength of the magnetic field

• Increasing the number of turns of the coil

• Replacing the coil with a coil of lower resistance

In a DC generator the current to the external circuit is delivered through the …

• coils.

• battery.

• slip rings.

• split rings (commutators).

The diagram above shows a current-carrying conductor lying in a uniform magnetic field directed to the right. The current flows into the page. Which ONE of the following arrows shows the direction of the force experienced by the conductor due to the magnetic field?

• 
• 
• 
• 

Some learners decided to build a small electrical generator in the laboratory. They then used this generator to investigate how the magnitude of the induced emf would change as the magnetic field strength changed.

Which ONE of the following is CORRECT regarding the variables for the investigation?

• DEPENDENT VARIABLE: Magnitude of induced emf

  INDEPENDENT VARIABLE: Number of turns of coil of generator

  CONTROL VARIABLE: Magnetic field strength

• DEPENDENT VARIABLE: Number of turns of coil of generator

  INDEPENDENT VARIABLE: Magnitude of induced emf

  CONTROL VARIABLE: Magnetic field strength

• DEPENDENT VARIABLE: Magnitude of induced emf

  INDEPENDENT VARIABLE: Magnetic field strength

  CONTROL VARIABLE: Number of turns of coil of generator

• DEPENDENT VARIABLE: Magnetic field strength

  INDEPENDENT VARIABLE: Number of turns of coil of generator

  CONTROL VARIABLE: Magnitude of induced emf

Which ONE of the following changes may lead to an increase in the emf of an AC generator without changing its frequency?

• Decrease the resistance of the coil.

• Increase the area of the coil.

• Increase the resistance of the coil.

• Decrease the speed of rotation.

The speed of rotation of the coils in an AC generator is increased. Which ONE of the following combinations of frequency and output voltage for the generator will occur as a result of the change?

• FREQUENCY: Increases

  OUTPUT VOLTAGE: Increases

• FREQUENCY: No change

  OUTPUT VOLTAGE: Increase

• FREQUENCY: Decrease

  OUTPUT VOLTAGE: Decrease

• FREQUENCY: Increase

  OUTPUT VOLTAGE: No change

The coils of an AC generator make one complete rotation. The resulting graph for the output emf is shown above. The position B on the graph is obtained when the plane of the coil is at an angle of … to the magnetic field.

• 0º

• 60º

• 90º

• 120º

The direction of induced emf or current is indicated by:

• Fleming’s left-hand rule

• Fleming’s right-hand rule

• Faraday’s law of electromagnetic induction

• Ampere’s swimming rule