Questions DC Motors and Generators.

Define electromagnetism.

• Study of electric circuits only.
• Interaction between electric currents and magnetic fields.
• Behaviour of static electric charges.
• None of the above.

What happens to a wire when current flows through it

• The magnetic field disappears.
• A magnetic field is created with concentric circles around the wire.
• The wire repels all magnetic objects.
• The wire becomes an insulator.

How can the strength of an electromagnet be increased?

• Decrease the current through the coil.
• Reduce the number of turns in the coil.
• Use a material like plastic as the core.
• Increase the current or number of turns in the coil.

What is the right-hand curl rule used for?

• Determining the direction of electric current.
• Determining the direction of the magnetic field around a conductor.
• Finding the strength of a magnetic field.
• Calculating electric resistance.

What happens if the direction of the current in a wire is reversed?

• The magnetic field remains unchanged
• The direction of the magnetic field reverses.
• The magnetic field becomes stronger.
• The current stops flowing.

What is electromagnetic induction?

• Generating an electric current using a chemical reaction.
• Generating emf in a conductor due to a changing magnetic field.
• Generating heat in a conductor.
• Storing electric charge in a coil.

What is the relationship between current and magnetic field strength in a straight wire?

• They are directly proportional.
• They are inversely proportional.
• There is no relationship.
• They are equal.

Faraday's Law states:

• Magnetic flux is inversely proportional to emf.
• Emf is directly proportional to the rate of change of magnetic flux.
• Magnetic fields cannot change.
• A moving coil cannot generate emf.

Lenz's Law helps determine:

• The direction of the induced emf.
• The magnitude of resistance in a coil.
• The strength of the magnetic field.
• The temperature of a conductor.

What increases the magnitude of the induced emf?

• Reducing the number of turns in the coil.
• Increasing the speed of change of the magnetic field.
• Decreasing the magnetic field strength.
• Keeping the coil stationary.