Olete.in – MCQs, Mock Tests & Government Job Prep | ECAT ECAT Physics Alternating Current Mcq Questions

An alternating current or voltage

1. fluctuates off and on
2. varies in magnitude alone
3. changes its direction again and again
4. changes its magnitude harmonically and reverses its direction of flow after regularly recurring intervals.

✅ Correct Answer: 3

A changing magnetic flux produces around itself an induced

1. Magnetic field
2. Electric field
3. Electromagnetic force
4. Artificial gravitational field

✅ Correct Answer: 3

Electromagnetic waves travel in free space with the speed of

1. ?-rays
2. Positive rays
3. Cathode rays
4. More than sound waves

✅ Correct Answer: 1

The direction of propagation of an electromagnetic waves is

1. Perpendicular to electric field
2. Perpendicular to both electric and magnetic field
3. Perpendicular to magnetic field
4. Parallel to electric and magnetic field

✅ Correct Answer: 2

An electromagnetic wave consists of

1. Electric and magnetic fields moving parallel to each other
2. Magnetic field moving with velocity of light in space
3. Electric field moving with velocity of light
4. Electric and magnetic fields moving perpendicular to each other

✅ Correct Answer: 4

Electromagnetic waves transport

1. Energy
2. Momentum
3. Mass
4. Heat

✅ Correct Answer: 1

Waves emitted from the antenna are

1. Sound waves
2. Electromagnetic waves
3. Radio waves
4. Modulated waves

✅ Correct Answer: 2

Electromagnetic waves emitted from antenna are

1. Stationary
2. Longitudinal
3. Transverse
4. All the above

✅ Correct Answer: 3

If capacitance of L-C circuit is made four times then frequency of the circuit becomes

1. Twice
2. One half
3. Four times
4. None

✅ Correct Answer: 2

A capacitor of capacitance 30?F is charged by a constant current of 10mA. If initially the capacitor was uncharged what is the time taken for the potential difference across the capacitor to reach 300V?

1. 0.9sec
2. 15 sec
3. 1.5x105sec
4. 0.9x102sec

✅ Correct Answer: 1

The value of the steady current which when flowing through the same resistor produces heat at the same rate as the mean rate of heat produced by the alternating current is

1. Average current
2. Sinusoidal current
3. r.m.s current
4. Net current

✅ Correct Answer: 3

To find the r.m.s value of an alternating current mathematically we need to have

1. Mean value of I2
2. Square root of mean value of I2
3. Square root of I2
4. Square of 1/2

✅ Correct Answer: 2

An alternating current of r.m.s value of 4.0 A and frequency 50Hz flows in a circuit containing 10? resistor. The peak current is then

1. 20A
2. 20.66A
3. 6.66A
4. 5.66A

✅ Correct Answer: 4

An alternating current is represented by the equation I = I?sin?t which of the following equation represents an alternating current of frequency and amplitude twice that of the above current?

1. I = 2I?Sin(?t/2)
2. I = 2I?Sin(2?t)
3. I = 2ISin?t
4. I = I?sin(2?t)

✅ Correct Answer: 2

pure resistor circuit the voltage and current are

1. Lagging each other
2. They are at 90? phase difference
3. They have zero phase difference
4. No phase difference

✅ Correct Answer: 3

In capacitive circuit the current

1. Lags behind voltage by ?/2
2. Is in phase with voltage
3. Opposite in phase of voltage by ?
4. Leads forward the voltage by ?/2

✅ Correct Answer: 4

A 100?F capacitor with 12V source in series having frequency 50Hz will offer a capacitive reactance of about

1. 32?
2. 62?
3. 50?
4. 100?

✅ Correct Answer: 1

If a glass plate is inserted in between the plate of a capacitor in series with a lighted bulb the brightness of the bulb

1. Remains same
2. Brightness increases
3. Brightness decreases
4. No light

✅ Correct Answer: 2

A pure variable resistor is connected in series with a pure capacitor of fixed capacitance. The impedance of the circuit

1. Remains
2. Becomes infinite
3. Becomes zero
4. Increases

✅ Correct Answer: 4

A wire of resistance R is coiled inductively so that its inductance is L. The impedance of the coil at a frequency of f is

1. (R+2?fL)
2. (R2+?2L2)
3. (R2+f2L2)
4. (R2+4?2f2L2)

✅ Correct Answer: 4

Ammeter connected in an AC circuit measures

1. Exact value of current
2. rms value of current
3. Net value of current
4. Peak value of current

✅ Correct Answer: 2

When a pure inductor of inductance L and a pure capacitor of capacitance C are connected in parallel to a sinusoidal potential difference V the potential difference across both L & C will be

1. Same
2. Different
3. At L will be more than at C
4. At L will be less than at C

✅ Correct Answer: 1

An alternating potential difference is connected across a pure resistor and the frequency of the supply is varied but the rms value of the voltage is kept constant. The mean rate of heat dissipated from the resistor is

1. Directly proportional to f
2. Directly proportional to ??f
3. Directly proportional to f2
4. Inversely proportional to f

✅ Correct Answer: 3

What is the self inductance of a coil in which an induced emf of 2V is set up when the current changes at the rate of 4 As-1?

1. 0.5 mH
2. 0.5H
3. 2.0H
4. 8.0H

✅ Correct Answer: 2

The frequency of a circuit consisting of a capacitance C and a resistor R is

1. C/R
2. R/C
3. 1/RC
4. 1/ ??RC

✅ Correct Answer: 3

A 10? electric heater is connected to a 220V 50Hz mains supply. What is the peak value of the potential difference across the heater element?

1. 220V
2. 220/ ??2V
3. 110V
4. 220 ??2V

✅ Correct Answer: 4

A choke is used as a resistance in

1. DC circuit
2. AC circuits
3. Both AC and DC circuit
4. Full wave rectifier circuit

✅ Correct Answer: 2

At resonance the value of the power factor in an L-C-R series circuit is

1. Zero
2. half
3. 1
4. not definite

✅ Correct Answer: 3

An A.C series circuit containing 4? resistance and 3-? inductive reactance. The impedance of the circuit is

1. 1?
2. 5?
3. 7?
4. 7/?2?

✅ Correct Answer: 2

An inductive coil has a resistance of 100?. When an AC signal of frequency 1000Hz is fed to the coil the applied voltage leads the current by 45?. What is the inductance of the coil?

1. 10mH
2. 12mH
3. 16mH
4. 20mH

✅ Correct Answer: 3

Choose the correct statement. In the case of AC circuit ohms law holds for

1. Peak values of voltage and current
2. Effective values of voltage and current
3. Instantaneous values of voltage and current
4. All of the above

✅ Correct Answer: 4

The phase angle between the voltage and the current in an AC circuit consisting of a resistance is

1. Zero
2. 45?
3. 90?
4. 180?

✅ Correct Answer: 1

In an LCR series circuit, if V is the effective value of the applied voltage VR is the voltage across R VL is the effective voltage across L & Vc is the effective voltage across C then

1. V = VR+VL+VC
2. V2 = VR2+VL2+VC2
3. V2 = VR2+(VL-VC)2
4. V2 = VL2+(VR-VC)2

✅ Correct Answer: 3

a voltage V = V? cos ?t is applied across a resistor of resistance R the average power dissipated per cycle in the resistor is given by

1. V?/?2R
2. V?/?2?R
3. V?2/?2R
4. V?2/?2?R

✅ Correct Answer: 3

Two identical coaxial circular loops carry equal currents in the same direction. If the loops approach each other the current in

1. Each increases
2. Each decreases
3. Each remains the same
4. One increases whereas that in the other decreases

✅ Correct Answer: 2

An inductor may store energy in

1. its electric field
2. its coils
3. its magnetic field
4. both electric and magnetic fields

✅ Correct Answer: 3

Tick the correct statement

1. the flight path of a vertically falling body appears straight to the stationary observer
2. the flight path of vertically falling body appears parabolic to an observer in uniform relative motion
3. all states of rest and motion are relative and there is no such thing as absolute motion
4. all the above

✅ Correct Answer: 4

Mark the wrong statement.

1. a frame of reference which is either at rest or moves with a constant velocity is called an inertial frame of reference
2. an un-accelerated frame of reference is called an inertial frame of reference
3. all the frames of reference in uniform rectilinear motion are equivalent
4. Newtons laws of motion are valid in an accelerated (non inertial) frame of reference

✅ Correct Answer: 4

The relativistic energy E is equivalent to relativistic mass given by

1. Ec2
2. E/c2
3. E/c
4. c2/E

✅ Correct Answer: 2

An observer shoots parallel to a meter stick at very high (relativistic) speed and finds that the length of meter stick is

1. greater than one meter
2. less than one meter
3. one meter
4. a foolish question

✅ Correct Answer: 2