Question

A charged particle is moving in a uniform, constant magnetic field. Which one of the following statements concerning the magnetic force exerted on the particle is false It does no work on the particle. It increases the speed of the particle. It changes the velocity of the particle. It can act only on a particle in motion. It does not change the kinetic energy of the particle. A circular current loop with radius of 0.100 m is located in the x-y plane. A magnetic field of strength 2.5 T makes an angle of 60 degree with the z-axis. If loop carries a current of 2.0 A, what is the magnitude of the magnetic force on the loop zero N 1.36 N 0.157 N 0.136 N 0.0785 N An electron moves through a region of crossed electric and magnetic fields. The electric field E = 3000 V/m and is directed straight down. The magnetic field B = 0.50 T and is directed to the left. For what velocity v of the electron into the paper will the electric force exactly cancel the magnetic force 6000 m/s 4500 m/s 3000 m/s 2000 m/s 1500 m/s A long, straight wire is in the same plane as a nonconducting loop. The wire carries an increasing current I in the direction shown in the figure. There will be a clockwise induced current in the loop. There will be a counterclockwise induced current in the loop. There will be no induced emf and no induced current. There will be a clockwise induced emf, but no induced current. There will be a counterclockwise induced emf, but no induced current. An AC generator consists of 6 turns of wire. Each turn has an area of 0.040 m^2. The loop rotates in a uniform magnetic field (B = 0.20 T) at a constant frequency of 50 Hz. What is the maximum induced emf 0.064 V 2.4 V 2.9 V 15 V 18V When an RLC series circuit is in resonance, its impedance is: pie/2 ohm -pie/2 ohm a maximum equal to its resistance zero

Answer 1

3.solution

option B is correct

Magnetic fields do no work, so they cannot change the kinetic energy of the particle, hence the speed cannot increase. The velocity (which is a vector) can change*, for the direction may change, but it's magnitude (the speed) cannot change.

* This happens when the particle is moving about in a circle, which actually happens in this situation. In this case, the direction of the particle changes, but the speed is constant

5.solution

The electric force = qE = eE for an electron. The force is upwards as the electron is negative.

The magnetic force = Bqv = Bev for an electron. Using Fleming's left t hand rule and remembering electron flow is opposite to conventional current flow (as electrons are negative), the direction of the force is downwards (so it will cancel the electric force).

When the two forces are equal eE = Bev, so v = E/B.

v = 3000 V/m / 2.0 T

v = 1500 m/s

7.solution

a) The induced EMF is given by the derivative of the magnetic flux x (-1). In this case, the flux is:
Flux = 6*A*B*cos(w*t), where:
A = 0.040 (m^2)
B = 0.20 (T)
w = 2*pi*60 (rad/sec)
So EMF = - (- N*A*B*w)
= 6*0.040*0.2*2*pi*60
= 18.09 sin(wt)
The maximum is 18.09 (V)

8.solution

(a) equal to resistance