Q. No.If \(n\), \(e\), \(\tau\) and \(m\) respectively represent the density, charge relaxation time and mass of the electron, then the resistance of a wire of length \(l\) and area of cross-section \(A\) will be:
1. \(\frac{ml}{ne^2\tau A}\)
2. \(\frac{m\tau^2A}{ne^2l}\)
3. \(\frac{ne^2\tau A}{2ml}\)
4. \(\frac{ne^2 A}{2m\tau l}\)
1. \(\frac{ml}{ne^2\tau A}\)
2. \(\frac{m\tau^2A}{ne^2l}\)
3. \(\frac{ne^2\tau A}{2ml}\)
4. \(\frac{ne^2 A}{2m\tau l}\)
The relaxation time in conductors :
1. Increases with the increase in temperature
2. Decreases with the increase in temperature
3. It does not depend on the temperature
4. All of the sudden changes at 400 K
Resistance of tungsten wire at 150°C is 133 Ω. Its resistance temperature coefficient is 0.0045/°C. The resistance of this wire at 500°C will be
1. 180 Ω
2. 225 Ω
3. 258 Ω
4. 317 Ω
Which of the following has a negative temperature coefficient of resistance?
1. C
2. Fe
3. Mn
4. Ag
A solenoid is at the potential difference of \(60~\text V\) and the current flows through it is \(15~\text A\) then the resistance of the coil will be:
1. \(4~\Omega\)
2. \(8~\Omega\)
3. \(0.25~\Omega\)
4. \(2~\Omega\)
All of the following statements are true except
1. Conductance is the reciprocal of resistance and is measured in Siemens
2. Ohm's law is not applicable at very low and very high temperatures
3. Ohm's law is applicable to semiconductors
4. Ohm's law is not applicable to electron tubes, discharge tubes and electrolytes
A steady current flows in a metallic conductor of non-uniform cross-section. The quantity/ quantities constant along the length of the conductor is/are :
1. Current, electric field and drift speed
2. Drift speed only
3. Current and drift speed
4. Current only
σ1 and σ2 are the electrical conductivities of Ge and Na respectively. If these substances are heated, then
1. Both σ1 and σ2 increase
2. σ1 increases and σ2 decreases
3. σ1 decreases and σ2 increases
4. Both σ1 and σ2 decrease
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