Physics - Electromagnetic Induction and Alternating Currents
Exam Duration: 45 Mins Total Questions : 30
Two identical coils each of inductance L are equivalent to a total inductance of 2H when connected in parallel.The value of L for each coil is:
- (a)
1H
- (b)
2H
- (c)
4H
- (d)
6H
The direction of induced e.m.f can be found by
- (a)
Fleming's left-hand rule and Lenz's law
- (b)
Fleming's right-hand rule
- (c)
Right hand thumb rule
- (d)
Maxwell's cork-screw rule
The parallel LC circuit acts as a simple harmonic oscillator due to the exchange of
- (a)
Kinetic and potential energy
- (b)
velocity of positive and negative charge
- (c)
electric and magnetic energy
- (d)
electric energy in C and magnetic energy in L.
Which one of the following statements is CORRECT?
- (a)
A transformer can work with both A.C and D.C
- (b)
A choke is used to reduce the current in an A.C circuit because it offers impedance
- (c)
A choke is used to reduce the current because it offers resistance to the passage of A.C in an electrical circuit
- (d)
An element from an electrolyte can be liberated by passing A.C
The admittance of an inductor is expressed as
- (a)
\(-\frac { i }{ \omega L } \)
- (b)
\(i\omega L\)
- (c)
\(-i\omega L\)
- (d)
\(\frac { i }{ \omega L } \)
Dimensions of admittance are
- (a)
\(M{ L }^{ 3 }{ T }^{ -3 }\quad { A }^{ -2 }\)
- (b)
\( {{M } ^ { -1 } { L }^{ -2 }{ T }^{ 3 } { A }^{ 2 }}\)
- (c)
\(M{ L }^{ 2 }{ T }^{ 3 }\quad { A }^{ -2 }\)
- (d)
\( {{M } ^ { -1 } { L }^{ -3 }{ T }^{ 4 } { A }^{ 2 }}\)
In case of step-up transformer,\({ I }_{ p }\)and \({ I }_{ s }\)are the current flowing in primary and secondary coils. then,
- (a)
\({ I }_{ p }<{ I }_{ s }\)
- (b)
\({ I }_{ p }>{ I }_{ s }\)
- (c)
\({ I }_{ p }={ I }_{ s }\)
- (d)
\({ I }_{ p }\)is independent of \({ I }_{ s }\)
In the case of an ideal step-down transformer
- (a)
The secondary wire is thinner
- (b)
The primary wire is thinner
- (c)
the two have the same thickness
- (d)
the thickness is no consideration
The number of turns in the primary and secondary windings of a transformer are in the ratio 1:2. the primary is connected to an a.c source of 50 volts at 50 Hz.The output at secondary coil is
- (a)
100 volts at 100 Hz
- (b)
2500 volts at 100 Hz
- (c)
100 volt at 50 Hz
- (d)
25 volt at 50 Hz
A saturated magnetic induction of one tesla is developed in a homogeneous sample of iron with relative permeability 2000. The energy density of the field with the sample is [\({ \mu }_{ 0 }=4\pi \times { 10 }^{ -7 }H{ m }^{ -1 }\)]
- (a)
\(398\quad J\quad { m }^{ -3 }\)
- (b)
\(1210\quad J\quad { m }^{ -3 }\)
- (c)
\(199\quad J\quad { m }^{ -3 }\)
- (d)
\(1011\quad J\quad { m }^{ -3 }\)
A capacitor C is charged as usual in a circuit which has a resistance R and e.m.f.E.After how many time constants will the energy stored in the capacitor equal 80% of the final value?
- (a)
5.0
- (b)
4.0
- (c)
3.0
- (d)
2.25
An electric bulb of 100 W is connected in parallel with an ideal inductor of 1H.The arrangement is connected to a 90 V battery through a switch.On pressing the switch
- (a)
bulb glows
- (b)
bulb glows after some time
- (c)
bulb does not glow
- (d)
bulb glows for a short time and then stops glowing
The number of turns of primary and secondary coils of a transformer are 5 and 10 respectively and mutual inductance of the transformer is 25H.now, the number of turns in primary and secondary are made 10 and 5 respectively.Mutual inductance of transformer will be
- (a)
25H
- (b)
12.5H
- (c)
50H
- (d)
6.25H
An e.m.f. of 15 V is applied in a circuit coil containing 5 henry inductance and 10 ohm resistance.The ratio of currents at time t=\(\infty \) and t=1 s, is
- (a)
\(\frac { { e }^{ 1/2 } }{ { e }^{ 1/2 }-1 } \)
- (b)
\(\frac { { e }^{ 2 } }{ { e }^{ 2 }-1 } \)
- (c)
1-\( { e }^{ -1 }\)
- (d)
\( { e }^{ -1 }\)
In an induction coil with resistance, the induced e.m.f. will be maximum, when
- (a)
the switch is put on, due to high resistance
- (b)
the switch is put off, due to high resistance
- (c)
the switch is put on, due to low resistance
- (d)
the switch is put off, due to low resistance
Quantity that remains unchanged in a transformer is
- (a)
voltage
- (b)
current
- (c)
frequency
- (d)
none of these
In an a.c. circuit containing only capacitance, the current
- (a)
leads voltage by \({ 180 }^{ \circ }\)
- (b)
remains in phase with voltage
- (c)
leads voltage by \({ 90 }^{ \circ }\)
- (d)
lags behind voltage by \({ 90 }^{ \circ }\)
For a varying current i=i,\(\cos { \omega t+{ i }_{ 2 } } \sin { \omega t } \),the r.m.s value of current will be
- (a)
\(\frac { 1 }{ \sqrt { 2 } } ({ i }_{ 1 }+{ i }_{ 2 })\)
- (b)
\(\frac { 1 }{ \sqrt { 2 } } ({ i }_{ 1 }+{ i }_{ 2 })^{2 }\)
- (c)
\(\frac { 1 }{ \sqrt { 2 } } \sqrt { { { i }_{ 1 } }^{ 2 }+{ { i }_{ 2 } }^{ 2 } } \)
- (d)
\(\frac { 1 }{ { 2 } } \sqrt { { { i }_{ 1 } }^{ 2 }+{ { i }_{ 2 } }^{ 2 } } \)
The resistor \({ R }_ {1 }\)dissipates power p when connected to a generator.If a resistor \({ R } _ { 2 }\)is inserted in series with \({ R }_ {1 }\),the power dissipated by \({ R }_ {1 }\)
- (a)
increases
- (b)
decreases
- (c)
remains the same
- (d)
may decrease or increase depending on values of \({ R }_ {1 }\) and \({ R } _ { 2 }\)
In L-C-R circuit, the power dissipation is through
- (a)
R
- (b)
L
- (c)
C
- (d)
all L, C and R
A closed planar wire loop of area A and arbitrary shape is placed in a uniform magnetic field of magnitude B, with its plane perpendicular to magnetic field. The resistance of the wire loop is R. The loop is now turned upside down by \(180^O\) so that its plane again becomes perpendicular to the magnetic field. The total charge that must have flowed through the wire ring in the process is
- (a)
\(<{AB\over R}\)
- (b)
\({AB\over R}\)
- (c)
\({2AB\over R}\)
- (d)
None of these
A horizontal straight wire 20 m long extending from East to West is falling with a speed of \(50\ ms^{-1}\), at right angles to the horizontal component of the earth's magnetic field \(0.30\times 10^{-4}\ Wbm^{-2}\). The instantaneous value of the emf induced in the wire will be
- (a)
6.0 mV
- (b)
3 mV
- (c)
4.5 mV
- (d)
1.5 mV
Two coaxial solenoids are made by winding thin insulated wire over a pipe of cross-sectional area \(A=10\ cm^2\) and length = 20 cm. If one of the solenoids has 300 turns and the other 400 turns, their mutual inductance is \(\mu_0=\ 4 \pi\times 10^{-7}\ TmA ^{-1}\)
- (a)
\(2.4 \pi \times 10^{-5}\ H\)
- (b)
\(4.8 \pi \times 10^{-4}\ H\)
- (c)
\(4.8 \pi \times 10^{-5}\ H\)
- (d)
\(2.4 \pi \times 10^{-4}\ H\)
An ideal coil of 10 H is connected in series with a resistance of 5\(\Omega\) and a battery of 5 V. 2s after the connection is made, the current flowing (in ampere in the circuit is)
- (a)
(1-e)
- (b)
e
- (c)
\(e^{-1}\)
- (d)
\((1-e^{-1})\)
Match the following following electrical appliances given in column I with the principle on which they works given in column II and select the correct option from the choices given below.
Column I | Column II |
A. AC Generator | 1. Mutual induction |
B. Transformer | 2. Torque experienced in magnetic field |
C. Moving coil Galvanometer | 3. Electromagnetic induction |
- (a)
A B C 2 3 1 - (b)
A B C 3 1 2 - (c)
A B C 3 2 1 - (d)
A B C 1 2 3