JEE Main Physics - Electromagnetic Induction and Alternating Currents
Exam Duration: 60 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
Three metalic loops of copper,platinum and sliver having exactly the same dimension,are rotating in a uniform magnetic field with the same angular velocity.The induced e.m.f is
- (a)
maximum in copper loop
- (b)
maximum in platinum loop
- (c)
maximum in sliver loop
- (d)
same in all the loops
An inductive load has
- (a)
the current laging behind the e.m.f
- (b)
the e.m.f laging behind the current
- (c)
the current and e.m.f in the same phase
- (d)
the current and e.m.f out of phase
A step up transformer develops 400V in the secondary coil for input of 200V a.c. the current in the transformer is.
- (a)
also stepped up
- (b)
same
- (c)
same but direction reversed
- (d)
Stepped down
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
Two single-turn circular loops with radii R and r<
- (a)
\(M=4\times { 10 }^{ -9 }H\)
- (b)
\(M=2{\pi}\times { 10 }^{ -7 }H\)
- (c)
\(M=4{\pi}\times { 10 }^{ -8 }H\)
- (d)
None of the above
The LRC circuits has L=10mH, C=1\(\mu \)F,R=3.3\(\Omega \) and a.c. supply as E(t)=\(\cos { \omega t } \).At resonance, the current amplitude is
- (a)
3.3 A
- (b)
0.15 A
- (c)
0.30 A
- (d)
None of these
The LRC circuit has L=10 mH,C=1\(\mu F\),R=3.3\(\Omega \) and a.c supply as E(t)=\(\cos { \omega t } \). The average power dissipated per period at resonance is
- (a)
0.30 \(\omega \)
- (b)
0.30 m\(\omega \)
- (c)
1.5 mV
- (d)
0.15\(\omega \)
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
5 cm long solenoid having 10 ohm resistance and 5mH inductance isjoined in a 10 V battery.At steady state the current through the solenoid in amperes will be
- (a)
5
- (b)
1
- (c)
2
- (d)
3
Two coils have a mutual inductance of 0.005 H.The current in the first coil changes as i=\({ i }_{ 0 }\sin { \quad \omega t } \) where \({ i }_{ 0 }\)=10A and \(\omega =100\quad \pi \) radian/sec. The maximum value of e.m.f. induced in the second coil is(in volts)
- (a)
\(2\pi\)
- (b)
\(5\pi\)
- (c)
\(\pi\)
- (d)
\(4\pi\)
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
A metal ring is held horizontally and bar magnet is dropped through the ring with its length along the axis of the ring.The accelerations of the falling magnet is
- (a)
equal to g
- (b)
less than g
- (c)
more than g
- (d)
depends on the diameter of ring and length of magnet
The number of turns in a secondary coil is twice the number of turns in primary.A leclanche cell of 1.5 V is connected across the primary.The voltage across secondary is
- (a)
1.5V
- (b)
3.0 volt
- (c)
240 volt
- (d)
zero
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 average power dissipation ina pure inductor on inductance L when a.c. is passing through it is
- (a)
\(\frac { 1 }{ 2 } { LI }^{ 2 }\)
- (b)
\(\frac { 1 }{ 4 } { LI }^{ 2 }\)
- (c)
Zero
- (d)
\( { LI }^{ 2 }\)
Electric field varies through a coil at circular cross-section at the rate of 2N/C per sec. The induced emf in the coil is \((A=2\ cm^2).\)
- (a)
\(4\times 10^{-4}\ T\)
- (b)
\(2\times 10^{-4}\ T\)
- (c)
\(10^{-9}\ T\)
- (d)
zero
The magnetic flux through a stationary loop with resistance R varies during interval of time T as \(\phi =at (T-t)\). The heat generated during this time neglecting the inductance of loop will be
- (a)
\(a^2T^3\over 3R\)
- (b)
\(a^2T^2\over 3R\)
- (c)
\(a^2T\over 3R\)
- (d)
\(a^2T^3\over R\)
An alternating current generator has an internal resistance \(R_g\) and an internal reactance \(X_g\) . It is used to supply power to a passive load consisting of a resistance \(R_g\) and a reactance \(X_1.\) For maximum power to be delivered from the generator to the load, the value of \(X_L\) is equal to
- (a)
zero
- (b)
\(X_g\)
- (c)
\(-X_g\)
- (d)
\(R_g\)
In a circuit, there is an inductor connected with an AC source. The power dissipation in one cycle is
- (a)
\(I^2_{rms}\times L\)
- (b)
\(V^r_{rms}\over X _L\)
- (c)
\(I_{rms}\times V_{rms}\)
- (d)
None of these
In AC circuit when AC ammeter is connected, it reads i current if a student uses DC ammeter in place of AC ammeter, the reading in the DC ammeter will be
- (a)
\(i/\sqrt2\)
- (b)
\(\sqrt2i\)
- (c)
0.637 i
- (d)
zero