Alternating Current

The core of any transformer is laminated so as to
1. reduce the energy loss due to eddy currents.
2. make it light weight.
3. make it robust and strong.
4. increase the secondary voltage.
If the secondary coil has less turns than the primary coil, then it is called
1. a step-down transformer.
2. a step-up transformer.
3. LCR circuit
4. Resonant circuit
Which quantity is increased in a step-up transformer?
1. Current
2. Voltage
3. Power
4. Frequency
A device called transformer works on the principle of
1. self-induction
2. resistance
3. mutual induction.
4. capacitance
The power factor varies between
1. 2 and 2.5
2. 3.5 to 5
3. 0 to 1
4. 1 to 2
Alternating voltage (V) is represented by the equation
In which of the following circuits , the maximum power dissipation is observed ?
1. Pure capacitive circuit
2. Pure inductive circuit
3. Pure resistive circuit
4. None of these
In series LCR circuit, the phase angle between supply voltage and current is
At resonant frequency the current amplitude in series LCR circuit is ______ and the impedance is _________.
1. maximum , minimum
2. minimum , maximum
3. zero , infinity
4. infinity , zero
The electric mains supply in our homes and offices use _______.
1. alternating current
2. direct current
3. Wattless current
4. Watt current
Ohm’s law, which for resistors, works well for
1. ac voltages only
2. dc voltages only
3. both ac and dc voltages
4. potential difference
The equation denotes
1. Faraday’s rule
2. Ohm’s law
3. Kirchhoff’s loop rule
4. Joule heating
The analysis of an AC circuit is facilitated by using
1. Impedance diagram
2. Phasor diagram
3. Network diagram
4. Circuit diagram
An interesting characteristic of the series RLC circuit is the phenomenon of
1. Impedance
2. Admittance
3. Resonance
4. bandwidth
The power factor is denoted by
1. cos φ
2. tan φ
3. sin ω
4. cos ω
In a purely inductive or capacitive circuit, cosφ = 0 and no power is dissipated even though a current is flowing in the circuit. In such cases, current is referred to as a
1. eddy current
2. alternating current
3. wattless current
4. direct current
In which device mechanical energy is transformed into electric energy ?
1. a motor
2. a converter
3. a transformer
4. a generator
The natural frequency of oscillations or resonant frequency in LC circuit is given by
Average value of ac over a complete cycle _________ .
1. 1
2. 0
3. 0.707
4. 0.5
Electric current that varies in magnitude continuously and reverses its direction periodically is known as _________ .
1. alternating current
2. direct current
3. eddy current
4. wattless current
At an airport, a person is made to walk through the doorway of a metal detector, for security reasons. Is she/he is carrying anything made of metal, the metal detector emits a sound. On what principle does this detector work?
1. flux leakage
2. pure resistance
3. resonance
4. mutual induction
Find the peak voltage if the household line voltage is 220 V .
1. 311 V
2. 440 V
3. 155 V
4. 44 V
The inductive reactance is 7.85 ohms and voltage source is 220 V.
The rms current in the circuit is
1. 38 A
2. 32 A
3. 28 A
4. 30 A
If the primary coil of a transformer has 100 turns and the secondary has 200 turns, a 220V input at 10A will step-up to ______ voltage
Output and ______ current.
1. 110 V at 20 A
2. 440 V output at 5.0 A
3. 110 V at 5 A
4. 440 V output at 20A
To reduce the resonant frequency in an LCR series circuit with a generator
1. the generator frequency should be reduced.
2. another capacitor should be added in parallel to the first.
3. the iron core of the inductor should be removed.
4. dielectric in the capacitor should be removed.
If a secondary coil has 40 turns, and, a primary coil with 20 turns is charged with 50 V of potential difference, then the potential difference in the secondary coil would be
1. 50 V in secondary coil
2. 25 V in secondary coil
3. 60 V in secondary coil
4. 100 V in secondary coil
An alternating voltage is connected in series with a resistance R and an inductance L If the potential drop across the resistance is 200 V and across the inductance is 150 V, then the applied voltage is
1. 350 V
2. 250 V
3. 500 V
4. 300 V
In a LCR circuit having L = 8.0 henry, C = 0.5 mF and R = 100 ohm in series. The resonance frequency in per second is
1. 600 radian
2. 600 Hz
3. 500 radian
4. 500 Hz
A 60 microfarad capacitor is connected to a 110 V, 60 Hz AC supply. What is the value of root mean square value of current in the circuit?
1. 1.49 ampere
2. 2.49 ampere
3. 3.62 ampere
4. 4.12 ampere
In a pure capacitive circuit if the frequency of ac source is doubled, then its capacitive reactance will be
1. remains same
2. doubled
3. halved
4. zero

Alternating Current

Quiz