Temperature dependence of resistivity ρ(T) of semiconductors, insulators, and metals is significantly based on the following factors:
 

1. number of charge carriers can change with temperature T
2. the time interval between two successive collisions can depend on T
3. length of material can be a function of T
4. mass of carriers is a function of T



Which of the above statements is correct?

1. (a, b)

2. (c, d)

3. (b, c)

4. (b, d)

Subtopic:  Derivation of Ohm's Law |
 76%
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The measurement of an unknown resistance R is to be carried out using a Wheatstone bridge. Two students perform an experiment in two ways. The first students take R2 = 10 Ω and R1 =5 Ω. The other student takes R2 =1000 Ω and R1 =500 Ω. In the standard arm, both take R3 = 5 Ω.

Both find R=R2R1R3=10 Ω within errors.

(a) The errors of measurement of the two students are the same.

(b) Errors of measurement do depend on the accuracy with which R2 and R1 can be measured.

(c) If the student uses large values of R2 and R1, the currents through the arms will be feeble. This will make the determination of the null point accurately more difficult.

(d) Wheatstone bridge is a very accurate instrument and has no errors of
measurement.

1. (a, c)

2. (c, d)

3. (b, c)

4. (c, d)

Subtopic:  Wheatstone Bridge |
 52%
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In a meter bridge, point D is a neutral point as shown in the figure.
 

a. The meter bridge can have no other neutral point for this set of resistances.
b. When the jockey contacts a point on the meter wire left of D, current flows to B from the wire.
c. When the jockey contacts a point on the meter wire to the right of D, current flows from B to the wire through the galvanometer.
d. When R is increased, the neutral point shifts to left.


                                    

Which of the above statements is correct?

1. (a, c)

2. (a, d)

3. (b, c)

4. (c, d)

Subtopic:  Meter Bridge & Potentiometer |
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Consider a current carrying wire (current I) in the shape of a circle. Note that as the current progresses along the wire, the direction of j (current density) changes in an exact manner, while the current I remains unaffected. The agent that is essentially responsible for it is:

1. source of emf
2. the electric field produced by charges accumulated on the surface of the wire
3. the charges just behind a given segment of wire which push them just the right way by repulsion
4. the charges ahead

Subtopic:  Current & Current Density |
 58%
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Two batteries of emf ε1 and ε2 (ε2>ε1) and internal resistances r1 and r2 respectively are connected in parallel as shown in the figure.

                                   

1. The equivalent emf εeq of the two cells is between ε1 and ε2. i.e, ε1<εeq<ε2

2. The equivalent emf εeq is smaller than ε1

3. The εeq is given by εeq=ε1+ε2 always

4. εeq is independent of internal resistances r1 and r2

Subtopic:  Grouping of Cells |
 59%
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A resistance R is to be measured using a meter bridge. A student chooses the standard resistance S to be 100 Ω. He finds the null point at l= 2.9 cm. He is told to attempt to improve accuracy. Which of the following is a useful way?
 

1. He should measure l1 more accurately
2. He should change S to 1000  Ω and repeat the experiment
3. He should change S to 3  Ω and repeat the experiment
4. He should give up hope of more accurate measurement with a meter bridge

Subtopic:  Meter Bridge & Potentiometer |
 51%
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Two cells of emf's approximately 5 V and 10 V are to be accurately compared using a potentiometer of length 400 cm.
 

1. The battery that runs the potentiometer should have a voltage of 8 V
2. The battery of the potentiometer can have a voltage of 15 V and R adjusted so that the potential drop across the wire slightly exceeds 10 V
3. The first portion of 50 cm of the wire itself should have a potential drop of 10 V
4. Potentiometer is usually used for comparing resistances and not voltages

Subtopic:  Meter Bridge & Potentiometer |
 72%
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A metal rod of length 10 cm and a rectangular cross-section of 1 cm x 1/2 cm is connected to a battery across opposite faces. The resistance will be:

 

1. maximum when the battery is connected across 1 cm x 1/2 cm faces.
2. maximum when the battery is connected across 10 cm x 1 cm faces.
3. maximum when the battery is connected across 10 cm x 1/2 cm faces.
4. same irrespective of the three faces.

Subtopic:  Derivation of Ohm's Law |
 58%
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Which of the following characteristics of electrons determines the current in a conductor?

1. Drift velocity alone

2. Thermal velocity alone

3. Both drift velocity and thermal velocity

4. Neither drift nor thermal velocity

Subtopic:  Current & Current Density |
 57%
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Kirchhoff's junction rule is a reflection of:

a. conservation of the current density vector
b. conservation of charge
c. the fact that the momentum with which a charged particle approaches a junction is unchanged (as a vector) as the charged particle leaves the junction
d. the fact that there is no accumulation of charges at a junction

Which of the above statements are correct?
1. b and c
2. a and c
3. b and d
4. c and d

Subtopic:  Kirchoff's Current Law |
 70%
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