Question 36
Which of the following is used in an electric power station to minimize the power loss in an electric power transmission?

ac generator
step-up transformer
step-down transformer
dc motor
Question 37
Which of the following electro-magnetic radiations has the shortest wavelength?

microwaves
x rays
gamma rays
radio waves
Question 38
A 0.35 m2 coil with 50 turns produces a maximum emf of 45 volts in a magnetic field of 0.4 Tesla. What is the speed of rotation of the coil?

18.4 rad/s
6.4 rad/s
3.2 rad/s
1.0 rad/s
Question 39
Which of the following is correct for the back emf in a motor?

The net emf across the motor is the sum of the back emf and the applied emf.
The net emf across the motor is the difference between applied emf and the back emf.
Back emf decreases as the coil in the motor rotates faster.
Increase of the back emf increases the current in the coil.
Question 40
Electric and magnetic fields are ___________ in nature in the electromagnetic waves.

oscillating
parallel
transverse
constant
Question 41
What do radio waves, micro waves, X rays, and gamma rays all have in common?

They are produced in the same way.
They are electromagnetic waves.
They are detected in the same way.
They store the same amount of energy.
Question 42
The maximum value of the ac current in a circuit is 2.50 A. What is the rms value of the current?

1.76 A
1.25 A
3.53 A
5.00 A

A 0.2 kg conductor of length 0.8 m carries 2 ampere current to the right in a magnetic field. What is the magnitude and the direction of the magnetic field acting on the conductor if the net force on the rod is zero? (Assume that the rod is hung by two insulating supports.)

A 0.35 m2 coil with 50 turns rotates at 5 radians per sec2 in a magnetic field of 0.6 Tesla. What is the value of the rms current in the coil if the coil has the resistance of 3.3 Ω?

A step-up transformer used in a car has a potential difference of 10 V across the primary coil with 12 turns. What is the current in the secondary coil of resistance 2.5 Ω if the number of turns in the secondary coil is 54 turns?

Question 22
A step-down transformer used on an 800 V line has 100 turns on the primary. What is the emf produced on the secondary coil if the turns on it are 40 turns?

200 V
320 V
2000 V
4000 V
Question 23
The maximum ac voltage in a circuit is 156 V. What is the rms voltage in the circuit?

312 V
221 V
110 V
78 V
Question 24
Which of the conversions is correct for an ac generator?

high emf to low emf and vice versa
direct current to alternating current
mechanical energy to electrical energy
electrical energy to mechanical energy
Question 25
The maximum current generated by an ac generator to a 30 Ω resistor is 5.2 A. What is the rms potential difference in the circuit?

156 V
110 V
78 V
70 V
Question 26
The operation of an electric motor depends on:

the Doppler effect
the photo electric effect
the magnetic force acting on a current-carrying conductor in a magnetic field
alignment of magnetic domains
Question 27
The wavelength of the electromagnetic waves is 500 nm. Which of following regions does it belong to?

visible light region
ultra violet region
infrared region
x ray region
Question 28
What is the wavelength of the electromagnetic wave whose frequency is 4 x 1016 Hz?

7.50 nm
750 nm
1.33 nm
133 nm
Question 29
The energy associated with the photon is 20 x 10-20 Hz. What is the frequency of the photon?

0.3 x 1014 Hz
3.0 x 1014 Hz
3.3 x 10 -14 Hz
0.3 x 10-14 Hz
Question 30
Which of the following statements is correct?

The magnetic field of an induced emf always increases the increasing/decreasing magnetic field.
Lenz’s law is used to find the average induced emf.
An induced electric field opposes the applied magnetic field.
The magnetic field of an induced current always opposes the increasing/decreasing magnetic field.
Question 32
A proton moving to the right enters the magnetic field perpendicular to the plane of paper acting outward. Which of the following is correct for the path of the proton?

It continues to go straight.
First it goes to the right, and then it returns to the left.
It bends upward.
It bends downward.
Question 33
A proton and an alpha particle (a cluster of two protons and two neutrons) moving with the same speed are shot into the magnetic field. The ratio of the force experienced by the proton to the alpha particle is:

2:1
1: 4
1:2
4:1
Question 34
The output of the ac generator is 70 V. What is the maximum value of the voltage produced by the generator?

90 V
70 V
49 V
35 V
Question 35
When a charge enters the magnetic field, what is the condition for the charge to experience the maximum force?

The charge must enter at an angle of 45° to the direction of the magnetic field.
The charge must enter parallel to the direction of the magnetic field.
The charge must enter at an angle of 90° to the direction of the magnetic field.
The charge must enter at an angle of 30° to the direction of the magnetic field.

What is the maximum emf output?

2) An AC generator has 85 rectangular loops on its armature. Each loop is 13 cm long and 7 cm wide. The armature rotates at 1200 rpm about an axis parallel to the long side. If the loop rotates in a uniform magnetic field of 0.4 T, which is perpendicular to the axis of rotation, what will be the maximum output voltage of this generator?

2)An ac generator consists of a 135-turn circular planar coil that is able to rotate between the poles of a magnet. The magnetic field is perpendicular to the rotational axis of the coil and has a magnitude of 0.125 T. The coil has a diameter of 0.117 m. What will the maximum emf generated by the coil if it is rotated at a rate of 62.5 rad/s?
Answer:11.3 V
Please help. I have been trying for over an hour. How are the answers derived?

(b) What is the instantaneous value of the emf in the coil at t = (π/30) s? Assume that the emf is zero at t = 0.
____V

(c) What is the smallest value of t for which the emf will have its maximum value?
____s

If she wanted to make the maximum emf output ten times larger by adding loops, how many should she use in total?

thank you!

Thanks!