Ohm's law, resistance and V-I characteristics — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Ohm's law states that, provided the temperature and other physical conditions remain unchanged, the current through a conductor is

• A. directly proportional to the potential difference across it
• B. inversely proportional to the potential difference across it
• C. independent of the potential difference across it
• D. proportional to the square of the potential difference across it

Question 2 · difficulty L2 · understanding

The Colour coding on a carbon resistor is shown in the given figure. The resistance value of the given resistor is :

• A. (5700 $$\pm$$ 285) $$\Omega$$
• B. (7500 $$\pm$$ 750) $$\Omega$$
• C. (5700 $$\pm$$ 375) $$\Omega$$
• D. (7500 $$\pm$$ 375) $$\Omega$$

Question 3 · difficulty L2 · understanding

A conducting wire of length 'l', area of cross-section A and electric resistivity $$\rho$$ is connected between the terminals of a battery. A potential difference V is developed between its ends, causing an electric current. If the length of the wire of the same material is doubled and the area of cross-section is halved, the resultant current would be :

• A. $$4{{VA} \over {\rho l}}$$
• B. $${3 \over 4}{{VA} \over {\rho l}}$$
• C. $${1 \over 4}{{VA} \over {\rho l}}$$
• D. $${1 \over 4}{{\rho l} \over {VA}}$$

Question 4 · difficulty L2 · understanding

For a conductor that obeys Ohm's law, the graph of potential difference V (y-axis) against current I (x-axis) at constant temperature is

• A. a parabola through the origin
• B. a straight line through the origin whose slope equals the resistance R
• C. a straight line not passing through the origin
• D. a straight line through the origin whose slope equals 1/R

Question 5 · difficulty L3 · understanding

A uniform metallic wire carries a current 2 A, when 3.4 V battery is connected across it. The mass of uniform metallic wire is 8.92 $$\times$$ 10$$^{-3}$$ kg, density is 8.92 $$\times$$ 10$$^{3}$$ kg/m$$^3$$ and resistivity is 1.7 $$\times$$ 10$$^{-8}~\Omega$$-$$\mathrm{m}$$. The length of wire is :

• A. $$l=100$$ m
• B. $$l=6.8$$ m
• C. $$l=5$$ m
• D. $$l=10$$ m

Question 6 · difficulty L3 · understanding

In the experiment of Ohm's law, a potential difference of 5.0 V is applied across the end of a conductor of length 10.0 cm and diameter of 5.00 mm. The measured current in the conductor is 2.00 A. The maximum permissible percentage error in the resistivity of the conductor is :

• A. 3.9
• B. 8.4
• C. 7.5
• D. 3.0

Question 7 · difficulty L3 · understanding

Resistance of a carbon resistor determined from colour codes is $$(22000 \pm 5 \%) \Omega$$. The colour of third band must be :

• A. Green
• B. Orange
• C. Yellow
• D. Red

Question 8 · difficulty L3 · understanding

The color code of a resistance is given below : The values of resistance and tolerance, respectively, are

• A. 47 k$$\Omega$$ , 10%
• B. 4.7 k$$\Omega$$ , 5%
• C. 470 $$\Omega$$ , 5%
• D. 470 k$$\Omega$$ , 5%

Question 9 · difficulty L4 · application

A uniform wire of resistance R is stretched (without change of volume) until its length doubles. Which statement about the new resistance and the resistivity is correct?

• A. The resistance becomes 2R; the resistivity doubles
• B. The resistance becomes 2R; the resistivity is unchanged
• C. The resistance becomes 4R; the resistivity is unchanged, since it depends only on the material and temperature
• D. The resistance becomes 4R; the resistivity becomes 4 times

Question 10 · difficulty L4 · application

Ohm's law fails for many materials and devices. Which set of deviations is correctly described?

• A. V ceases to be proportional to I only in metals; diodes obey Ohm's law; GaAs is ohmic
• B. All three deviations occur only at absolute zero
• C. The only deviation possible is a change of slope with temperature
• D. V ceases to be proportional to I (e.g. a heated filament); the relation between V and I depends on the sign of V (e.g. a diode passes current for one polarity only); the relation is not unique - there is more than one value of V for the same current (e.g. GaAs, which shows a region of negative resistance)