Conductivity and Resistivity

Q. When $5V$ potential difference is applied across a wire of length $10cm,$ the drift speed of electrons is $2.5\times {10}^{–4}m/s.$ If the electron density in the wire is $8\times {10}^{28}/m^3$, then resistivity of the material is close to

1. $1.6\times {10}^{-7}\Omega m$
2. $1.6\times {10}^{-5}\Omega m$
3. $1.6\times {10}^{-6}\Omega m$
4. $1.6\times {10}^{-8}\Omega m$

Q. Iron-man needs a better suit to resist Thor’s lightning. What should he change to do this, given that he can’t change the dimensions (size and shape) of the suit.

1. Change the material of the suit.
2. Change the colour of the suit.
3. Change the batteries of the suit.
4. Change the name of the suit.

Q. For whatever reason, the relaxation time of a conductor increases by a factor of 2 and the number of electrons per unit volume decreases by a factor of 3. Given all other factors remain the same, the new conductivity changes by what factor?

1. $\frac{1}{6}$
2. $\frac{2}{3}$
3. $6$
4. $\frac{3}{2}$

Q.

The specific resistance of manganin is

$50\times {10}^{-8}\Omega m$.

The resistance of a manganin cube having length

50 cm is

1. ${10}^{-6}\Omega$
2. $2.5\times {10}^{-5}\Omega$
3. ${10}^{-8}\Omega$
4. $5\times {10}^{-4}\Omega$

Q. Following figure shows cross-sections through three long conductors of the same length and material, with square cross-section of edge lengths as shown. Conductor B will fit snugly within conductor A, and conductor C will fit snugly within conductor B. Relationship between their end to end resistance is

1. $R_A=R_B=R_C$
2. $R_A>R_B>R_C$
3. Information is not sufficient
4. $R_A<R_B<R$

Q. What is the unit of conductivity and resistivity respectively?

1. Ohm, mho
2. Mho, ohm
3. Ohm m, mho/m
4. Mho/m, ohm m

Q. The conductivity of a material is 5 mho/m. What is it’s resistivity?

1. None of these.
2. 5 ohm m
3. 0.2 ohm m
4. 25 ohm m

Q. Masses of three wires are in the ratio 1 : 3 : 5 and their lengths are in the ratio 5 : 3 : 1. The ratio of their electrical resistance is

1. 1 : 3 : 5
2. 5 : 3 : 1
3. 1 : 15 : 125
4. 125 : 15 : 1

Q. Length of a hollow tube is 5m, it’s outer diameter is 10 cm and thickness of it’s wall is 5 mm. If resistivity of the material of the tube is $1.7\times {10}^{-8}\Omega m$ then the resistance of the tube will be

1. None of these
2. $5.6\times {10}^{-5}\Omega$
3. $2\times {10}^{-5}\Omega$
4. $4\times {10}^{-5}\Omega$

Q. A material has a resistivity of 5 ohm m. The potential difference across the material was increased by a factor of 10. What is the new resistivity?

1. 5 ohm m
2. 50 ohm m
3. 500 ohm m
4. 0.5 ohm m