Physics Electricity and Magnetism 3

Question 1

A long straight wire carries 5 A of current. What is the magnetic field at a distance of 0.1 m from the wire? (μ₀ = 4π×10⁻⁷ T·m/A)

Accepted Answer

1×10⁻⁵ T

Answer

B = μ₀I/(2πr) = (4π×10⁻⁷ × 5)/(2π × 0.1) = 10⁻⁵ T.

Question 2

Which of the following best describes a diamagnetic material?

Accepted Answer

Weakly repelled by magnetic fields

Answer

Diamagnetic materials have a small negative susceptibility and are weakly repelled by external magnetic fields.

Question 3

An EMF of 20 V is induced in a coil when the current changes at a rate of 4 A/s. What is the self-inductance of the coil?

Accepted Answer

5 H

Answer

EMF = L(dI/dt), so L = EMF/(dI/dt) = 20/4 = 5 H.

Question 4

In a series RLC circuit at resonance, the impedance is:

Accepted Answer

Equal to R only

Answer

At resonance X_L = X_C, so they cancel and the total impedance Z = R.

Question 5

A proton moves east in a uniform magnetic field directed north. In which direction is the magnetic force on the proton?

Accepted Answer

Upward

Answer

Using F = qv×B with v east (+x) and B north (+y), F = q(x̂ × ŷ) = qẑ, which is upward.

Physics Practice Test