Conductivity and Resistivity

Q.

A glass wind screen whose inclination with the vertical can be changed is mounted on a car. The car moves horizontally with a speed of 2 m/s. At what angle $\alpha$ with the vertical should the screen be placed so that the rain drops falling downwards with velocity 6 m/s strike the windscreen perpendicularly?

1. 

2. 

3. 

4. 

Q. 122.The resistance of a bulb filament is 100 ohm at a temperature of 100 degree celsius. If its temperature coefficient of resistance be 0.005 per degree celsius, its resistance will become 200 ohm at at emperature of

Q. Resistance of a cube .

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. A wire of length $5\text{m}$ and radius $1\text{mm}$ has resistance of $1\Omega$. What length of the same material at the same temperature, and of radius $2\text{mm}$ will also have a resistance of $1\Omega$ ?

1. $1.25\text{m}$
2. $2.5\text{m}$
3. $10\text{m}$
4. $20\text{m}$

Q. Two metal wires of identical dimensions are connected in series. If ${\delta }_1$ and ${\delta }_2$ are the conductivities of the metal wires respectively, the effective conductivity of the combination is

1. $\frac{2{\delta }_1{\delta }_2}{{\delta }_1+{\delta }_2}$
2. $\frac{{\delta }_1+{\delta }_2}{2{\delta }_1+{\delta }_2}$
3. $\frac{2{\delta }_1+{\delta }_2}{{\delta }_1+{\delta }_2}$
4. $\frac{{\delta }_1{\delta }_2}{{\delta }_1+{\delta }_2}$

Q. Find the resistance of a hollow sphere whose inner surface (radius :a) and outer surface (radius b) are connected to a p.d E($\rho$:resistivity)

1. $\frac{\rho (b-a)}{4\pi ab}$
2. $\frac{\rho ab}{4\pi (b-a)}$
3. $\frac{\rho (b+a)}{4\pi ab}$
4. $\frac{\rho ab}{4\pi (b+a)}$

Q. Explain the importance of the depletion region in a p-n junction diode.

Q. Dimensions of a block are $1cm\times 1cm\times 100cm$. If specific resistance of its material is $3\times {10}^{-7}$ ohm - m, then the resistance between it’s opposite rectangular faces is

1. $3\times {10}^{-9}$ ohm
2. $3\times {10}^{-7}$ ohm
3. $3\times {10}^{-5}$ ohm
4. $3\times {10}^{-3}$ ohm

Q.

This section contains 1 Assertion-Reason type question, which has 4 choices (a), (b), (c) and (d) out of which ONLY ONE is correct.
इस खण्ड में 1 कथन-कारण प्रकार का प्रश्न है, जिसमें 4 विकल्प (a), (b), (c) तथा (d) दिये गये हैं, जिनमें से केवल एक सही है।

A : Electric power is transmitted from power stations via transmission cables at high voltage.
A : विद्युत शक्ति का संचरण पावर स्टेशन से उच्च वोल्टता पर संचरण केबल द्वारा किया जाता है।

R : Power wasted in connecting wires is $P_C=I^2{R}_C=\frac{P^2{R}_C}{V^2}$.
R : संयोजी तारों में शक्ति का अपव्यय $P_C=I^2{R}_C=\frac{P^2{R}_C}{V^2}$ है।

1. Both (A) and (R) are true and (R) is the correct explanation of (A)
   
   (A) तथा (R) दोनों सही हैं तथा (R), (A) का सही स्पष्टीकरण है
2. Both (A) and (R) are true but (R) is not the correct explanation of (A)
   
   (A) तथा (R) दोनों सही हैं लेकिन (R), (A) का सही स्पष्टीकरण नहीं है
3. (A) is true but (R) is false
   
   (A) सही है लेकिन (R) गलत है
4. (A) is false but (R) is true
   
   (A) गलत है लेकिन (R) सही है

Q. Two wires of same dimensions but different resistivities ${\rho }_1$ and ${\rho }_2$ are connected in series. The equivalent resistivity of the combination is

1. $\sqrt{{\rho }_1{\rho }_2}$
2. ${\rho }_1+{\rho }_2$
3. $\frac{{\rho }_1+{\rho }_2}{2}$
4. None of the above

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. 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