Current Electricity · JEE Main previous year questions

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2006 6 questions

Q742006 · 29 Apr 2006 · Shift 1
In an $A C$ generator, a coil with $N$ turns, all of the same area $A$ and total resistance $R$ , rotates with frequency $ω$ in a magnetic field $B$ . The maximum value of $e m f$ generated in the coil is
1. A. $N . A . B . R . ω$
2. B. $N . A . B$
3. C. $N . A . B . R .$
4. D. $N . A . B . ω$
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Answer: D
Q772006 · 29 Apr 2006 · Shift 1
1. A. $1/ e A$
2. B. $e A$
3. C. $0.1 A$
4. D. $1 A$
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Answer: A
Q902006 · 29 Apr 2006 · Shift 1
A material 'B' has twice the specific resistance of 'A'. A circular wire made of 'B' has twice the diameter of a wire made of 'A'. Then for the two wires to have the same resistance, the ratio $ℓ_{B} / ℓ_{A}$ of their respective lengths must be
1. A.2
2. B.1
3. C. $\frac{1}{2}$
4. D. $\frac{1}{4}$
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Answer: A
Q912006 · 29 Apr 2006 · Shift 1
The Kirchhoff's first law ( $\sum i = 0$ ) and second law ( $\sum i R = \sum E$ ), where the symbols have their usual meanings, are respectively based on
1. A.conservation of charge, conservation of energy
2. B.conservation of charge, conservation of momentum
3. C.conservation of energy, conservation of charge
4. D.conservation of momentum, conservation of charge
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Answer: A

2005 10 questions

Q822005 · 28 Apr 2005 · Shift 1
A bullet fired into a fixed target loses half of its velocity after penetrating $3 cm$ . How much further it will penetrate before coming to rest assuming that it faces constant resistance to motion?
1. A. $2.0 cm$
2. B. $3.0 cm$
3. C. $1.0 cm$
4. D. $1.5 cm$
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Answer: C
Q1172005 · 28 Apr 2005 · Shift 1
1. A. $100Ω$
2. B. $200Ω$
3. C. $1000Ω$
4. D. $500Ω$
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Answer: A
Q1182005 · 28 Apr 2005 · Shift 1
A moving coil galvanometer has 150 equal divisions. Its current sensitivity is 10-divisions per milliampere and voltage sensitivity is 2 divisions per millivolt. In order that each division reads 1 volt, the resistance in $o hm s$ needed to be connected in series with the coil will be -
1. A. $1 0^{5}$
2. B. $1 0^{3}$
3. C. $9995$
4. D. $99995$
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Answer: C
Q1192005 · 28 Apr 2005 · Shift 1
Two sources of equal $e m f$ are connected to an external resistance $R$ . The internal resistances of the two sources are $R_{1}$ and $R_{2} (R_{2} > R_{1})$ . If the potential difference across the source having internal resistance $R_{2}$ is zero, then
1. A. $R = R_{2} - R_{1}$
2. B. $R = R_{2} \times (R_{1} + R_{2}) / (R_{2} - R_{1})$
3. C. $R = R_{1} R_{2} / (R_{2} - R_{1})$
4. D. $R = R_{1} R_{2} / (R_{1} - R_{2})$
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Answer: A
Q1212005 · 28 Apr 2005 · Shift 1
The resistance of hot tungsten filament is about 10 times the cold resistance. What will be resistance of $100 W$ and $200 V$ lamp when not in use ?
1. A. $20Ω$
2. B. $40Ω$
3. C. $200Ω$
4. D. $400Ω$
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Answer: B
Q1222005 · 28 Apr 2005 · Shift 1
An energy source will supply a constant current into the load if its internal resistance is
1. A.very large as compared to the load resistance
2. B.equal to the resistance of the load
3. C.non-zero but less than the resistance of the load
4. D.zero
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Answer: A
Q1292005 · 28 Apr 2005 · Shift 1
A circuit has a resistance of $12 ohm$ and an impedance of $15 ohm$ . The power factor of the circuit will be
1. A. $0.4$
2. B. $0.8$
3. C. $0.125$
4. D. $1.25$
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Answer: B
Q1302005 · 28 Apr 2005 · Shift 1
A coil of inductance $300 mH$ and resistance $2 Ω$ is connected to a source of voltage $2 V$ . The current reaches half of its steady state value in
1. A. $0.1 s$
2. B. $0.05 s$
3. C. $0.3 s$
4. D. $0.15 s$
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Answer: A
Q1422005 · 28 Apr 2005 · Shift 1
In a full wave rectifier circuit operating from $50 Hz$ mains frequency, the fundamental frequency in the ripple would be
1. A. $25 Hz$
2. B. $50 Hz$
3. C. $70.7 Hz$
4. D. $100 Hz$
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Answer: D
Q1462005 · 28 Apr 2005 · Shift 1
In a potentiometer experiment the balancing with a cell is at length $240 cm$ . On shunting the cell with a resistance of $2Ω$ , the balancing length becomes $120 cm$ . The internal resistance of the cell is
1. A. $0.5Ω$
2. B. $1Ω$
3. C. $2Ω$
4. D. $4Ω$
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Answer: C

2004 10 questions

Q1072004 · 24 Apr 2004 · Shift 1
1. A. $4 A$
2. B. $2 A$
3. C. $1 A$
4. D. $6 A$
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Answer: A
Q1082004 · 24 Apr 2004 · Shift 1
The resistance of the series combination of two resistances is $S$ . When they are joined in parallel the total resistance is $P$ . If $S = n P$ then the minimum possible value of $n$ is
1. A. $2$
2. B. $3$
3. C. $4$
4. D. $1$
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Answer: C
Q1092004 · 24 Apr 2004 · Shift 1
An electric current is passed through a circuit containing two wires of the same material, connected in parallel. If the lengths and radii are in the ratio of $\frac{4}{3}$ and $\frac{2}{3}$ , then the ratio of the current passing through the wires will be
1. A. $8/9$
2. B. $1/3$
3. C. $3$
4. D. $2$
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Answer: B
Q1102004 · 24 Apr 2004 · Shift 1
In a meter bridge experiment null point is obtained at $20 cm$ , from one end of the wire when resistance $X$ is balanced against another resistance $Y$ . If $X < Y$ , then where will be the new position of the null point from the same end, if one decides to balance a resistance of $4 X$ against $Y$
1. A. $40 cm$
2. B. $80 cm$
3. C. $50 cm$
4. D. $70 cm$
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Answer: C
Q1152004 · 24 Apr 2004 · Shift 1
The Kirchhoff's first law $(\sum i = 0)$ and second law $(\sum i R = \sum E)$ , where the symbols have their usual meanings, are respectively based on
1. A.conservation of charge, conservation of momentum
2. B.conservation of energy, conservation of charge
3. C.conservation of momentum, conservation of charge
4. D.conservation of charge, conservation of energy
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Answer: D
Q1162004 · 24 Apr 2004 · Shift 1
A material $^{'} B^{'}$ has twice the specific resistance of $^{'} A^{'}$ . A circular wire made of $^{'} B^{'}$ has twice the diameter of a wire made of $^{'} A^{'}$ . Then for the two wires to have the same resistance, the ratio $l_{B} / l_{A}$ of their respective lengths must be
1. A. $1$
2. B. $\frac{1}{2}$
3. C. $\frac{1}{4}$
4. D. $2$
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Answer: D
Q1252004 · 24 Apr 2004 · Shift 1
In an $L C R$ series $a . c .$ circuit, the voltage across each of the components, $L, C$ and $R$ is $50 V$ . The voltage across the $L . C$ combination will be :
1. A. $100 V$
2. B. $502$
3. C. $50 V$
4. D. $0 V$ (zero)
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Answer: D
Q1262004 · 24 Apr 2004 · Shift 1
A coil having $n$ turns and resistance $R Ω$ is connected with a galvanometer of resistance $4 R Ω$ . This combination is moved in time $t$ seconds from a magnetic field $W_{1}$ weber to $W_{2}$ weber. The induced current in the circuit is
1. A. $\frac{( W _{2} - W _{1} )}{R n t}$
2. B. $- \frac{n ( W _{2} - W _{1} )}{5 R t}$
3. C. $- \frac{( W _{2} - W _{1} )}{5 R n t}$
4. D. $- \frac{n ( W _{2} - W _{1} )}{R t}$
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Answer: B
Q1272004 · 24 Apr 2004 · Shift 1
In a uniform magnetic field of induction $B$ a wire in the form of a semicircle of radius $r$ rotates about the diameter of the circle with an angular frequency $ω$ . The axis of rotation is perpendicular to the field. If the total resistance of the circuit is $R$ , the mean power generated per period of rotation is
1. A. $\frac{( B π r ω ) ^{2}}{2 R}$
2. B. $\frac{( B π r ^{2} ω ) ^{2}}{8 R}$
3. C. $\frac{B π r ^{2} ω}{2 R}$
4. D. $\frac{( B π r ω ^{2} ) ^{2}}{8 R}$
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Answer: B
Q1392004 · 24 Apr 2004 · Shift 1
A piece of copper and another of germanium are cooled from room temperature to $77 K$ , the resistance of
1. A.copper increases and germanium decreases
2. B.each of them decreases
3. C.each of them increases
4. D.copper decreases and germanium increases
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Answer: D

2002 5 questions

Q1172002 · 27 Apr 2002 · Shift 1
If an ammeter is to be used in place of a voltmeter, then we must connect with the ammeter a
1. A.low resistance in parallel
2. B.high resistance in parallel
3. C.high resistance in series
4. D.low resistance in series
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Answer: C