Understanding Energy in Magnetic Fields

What is a key difference between permanent magnets and electromagnets?

• Permanent magnets have a constant magnetic field, while electromagnets need a current.

• Electromagnets store energy without a magnetic field.

• Electromagnets have a constant magnetic field without needing a current.

• Permanent magnets require an electric current to generate a magnetic field.

What does the negative sign in the EMF equation indicate?

• The induced voltage is in the same direction as the current change.

• The induced voltage is unrelated to current change.

• The induced voltage is always positive.

• The induced voltage is opposite to the rate of change of current.

How is power calculated in the context of an inductor?

• By subtracting the current from the induced voltage.

• By adding the induced voltage to the current.

• By multiplying the induced voltage by the current.

• By dividing the induced voltage by the current.

What is the relationship between current and energy stored in an inductor?

• Energy is directly proportional to the current.

• Energy is inversely proportional to the current.

• Energy is unrelated to the current.

• Energy is directly proportional to the square of the current.

In the worked example, what is the energy stored in an inductor with 40 H inductance and 2 A current?

• 160 joules

• 40 joules

• 20 joules

• 80 joules