Paper 1 Magnetic Force Drills

Q1

The force on a current-carrying wire in a magnetic field is maximum when current is

A. parallel to the field.
B. perpendicular to the field.
C. zero.
D. opposite to electron drift only.

Q2

For a straight wire, magnetic force magnitude is

A. $F=BIL\sin \theta$.
B. $F=Bqv\cos \theta$.
C. $F=EQ$.
D. $F=mv/r$.

Q3

The magnetic force on a moving charge is zero when velocity is

A. perpendicular to field.
B. parallel to field.
C. at $45^{\circ }$.
D. large.

Q4

Magnetic force on a moving charge is always perpendicular to

A. velocity only.
B. field only.
C. both velocity and field components involved.
D. weight only.

Q5

For a charge moving perpendicular to a uniform magnetic field, the path can be circular because magnetic force supplies

A. tangential acceleration.
B. centripetal acceleration.
C. gravitational acceleration.
D. electric potential.

Q6

The radius of circular motion of charge $q$ is

A. $r=mv/(Bq)$ for perpendicular motion.
B. $r=Bq/(mv)$.
C. $r=v/Bqm$.
D. $r=BE/q$.

Q7

A velocity selector with crossed fields passes undeflected particles when

A. $qE=qvB$.
B. $E=qB/v$.
C. $v=EB$.
D. $v=qE/B$.

Q8

The force between parallel currents in the same direction is

A. repulsive.
B. attractive.
C. zero always.
D. electric only.

Q9

Fleming left-hand rule is used for

A. generator induced emf.
B. motor force direction.
C. charging capacitors.
D. refraction.

Q10

A magnetic field does no work on a charged particle because force is

A. parallel to velocity.
B. opposite to velocity.
C. perpendicular to velocity.
D. zero always.

Q11

For a negative charge, magnetic force direction is

A. same as for positive charge.
B. opposite to that for a positive charge with same velocity.
C. always upward.
D. always zero.

Q12

If $B$ doubles and $I$, $L$, $\theta$ are unchanged, force on a wire

A. halves.
B. doubles.
C. quadruples.
D. is unchanged.

Q13

For a wire parallel to the field, $\theta =0$ and force is

A. $BIL$.
B. $0$.
C. $BIL/2$.
D. $qvB$.

Q14

The SI unit tesla is equivalent to

A. $\mathrm{N}{\mathrm{A}}^{-1}{\mathrm{m}}^{-1}$.
B. $\mathrm{N}{\mathrm{C}}^{-1}$.
C. $\mathrm{V}{\mathrm{m}}^{-1}$.
D. $\mathrm{J}\mathrm{k}{\mathrm{g}}^{-1}$.

Q15

A current balance can measure magnetic flux density by measuring

A. mass change/force on known current length.
B. temperature only.
C. capacitance.
D. frequency only.

Q16

In circular motion in a magnetic field, speed remains constant because

A. force is radial.
B. force is tangential.
C. field is zero.
D. charge disappears.

Q17

If velocity has a component parallel to $\vec{B}$, that component

A. is affected by magnetic force.
B. is unchanged by magnetic force.
C. becomes zero instantly.
D. reverses every cycle.

Q18

Helical motion occurs when velocity is

A. entirely perpendicular to $\vec{B}$.
B. entirely parallel to $\vec{B}$.
C. partly parallel and partly perpendicular to $\vec{B}$.
D. zero.

Q19

The motor effect is the force on

A. a current-carrying conductor in magnetic field.
B. a stationary neutral object only.
C. light through a slit.
D. a capacitor plate only.

Q20

The force per unit length between two long parallel currents depends on

A. both currents and separation.
B. capacitance only.
C. temperature only.
D. voltage only.