# 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 $$R_2=10~\Omega$$ and $$R_1=5~\Omega$$. The other student takes $$R_2=1000~\Omega$$ ${\mathrm{}}_{}$and $$R_1=500~\Omega$$. In the standard arm, both take $$R_3=5~\Omega$$. Both find $$R = \dfrac{R_{2}}{R_{1}} R_{3} = 10 ~ \Omega$$ 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 $$R_2$$ and $$R_1$$ can be measured. (c) If the student uses large values of $$R_2$$ and $$R_1$$, 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.   Choose the correct option:  1. (a, c) 2. (c, d) 3. (b, c) 4. (c, d)

Subtopic:  Wheatstone Bridge |
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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 $$\text{I}$$) in the shape of a circle. Note that as the current progresses along the wire, the direction of $$\text{j}$$ (current density) changes in an exact manner, while the current $$\text{I}$$ 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 |
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Two batteries of emf and internal resistances respectively are connected in parallel as shown in the figure.

 1 The equivalent emf ${\mathrm{\epsilon }}_{\mathrm{eq}}$ of the two cells is between 2 The equivalent emf ${\mathrm{\epsilon }}_{\mathrm{eq}}$ is smaller than ${\mathrm{\epsilon }}_{1}$ 3 The ${\mathrm{\epsilon }}_{\mathrm{eq}}$ is given by ${\epsilon }_{eq}={\epsilon }_{1}+{\epsilon }_{2}$ always 4 ${\mathrm{\epsilon }}_{\mathrm{eq}}$ is independent of internal resistances
Subtopic:  Grouping of Cells |
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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 $\mathrm{\Omega }$. 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 |
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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 |
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A metal rod of length 10 cm and a rectangular cross-section of  $$1~ \text {cm} \times 1/2~ \text {cm}$$ is connected to a battery across opposite faces. The resistance will be:

 1 maximum when the battery is connected across$$1~ \text {cm} \times 1/2~ \text {cm}$$ faces. 2 maximum when the battery is connected across $$10~ \text {cm} \times 1~ \text {cm}$$ faces. 3 maximum when the battery is connected across $$10~ \text {cm} \times 1/2~ \text {cm}$$ faces. 4 same irrespective of the three faces.

Subtopic:  Derivation of Ohm's Law |
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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 |
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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 |
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Consider a simple circuit shown in the figure. $$R'$$ stands for variable resistance. $$R'$$ can vary from $$R_0$$ to infinity. $$r$$ is the internal resistance of the battery $$(r<<R<<R_0)$$.

 (a) Potential drop across $$AB$$ is nearly constant as $$R'$$ is varied. (b) Current through $$R'$$ is nearly constant as $$R'$$ is varied. (c) Current $$I$$ depends sensitively on $$R'$$. (d) $$I \geq { \dfrac V {r+R}}$$ always.

Which among the following statements is correct?

 1 (a, c) 2 (a, d) 3 (b, d) 4 (c, d)
Subtopic:  EMF & Terminal Voltage |
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