Semiconductors and Superconductors

Q. The electron concentration in an $n-$type semiconductor is the same as the hole concentration in a $p-$type semiconductor. An external field (electric) is applied across each of them. Compare the currents in them

1. No current will flow in $p-$type, but current will only flow in $n-$type.
2. Current in $n-$type $=$ current in $p$-type
3. Current in $p-$type $>$ current in $n-$type
4. Current in $n-$type $>$ current in $p-$type.

Q. Mobility of electrons in a semiconductor is defined as the ratio of their drift velocity to the applied electric field. If, for an $n-\text{type}$ semiconductor, the density of electrons is ${10}^{19}{\text{m}}^{-3}$ and their mobility is $1.6{\text{m}}^2{\text{V}}^{-1}{\text{s}}^{-1}$ then the resistivity of the semiconductor (since it is an $n-\text{type}$ semiconductor contribution of holes is ignored) is close to:

1. $2\Omega \text{m}$
2. $4\Omega \text{m}$
3. $0.4\Omega \text{m}$
4. $0.2\Omega \text{m}$

Q.

Why Earth behave like a magnet? Explain magnetic elements of earth at a place giving expressions.

Q.

Q. A wire of length L and resistance R is stretched to get the radius of cross section halved. What is the new resistance of the wire ?

Q. A copper wire is stretched to make it $0.5\%$ longer. The percentage change in its electrical resistance if its volume remains unchanged is:

1. $2.5\%$
2. $1.0\%$
3. $0.5\%$
4. $2.0\%$

Q.

The temperature coefficient of resistance of a semiconductor

1. is always poistive

2. is always negative

3. is zero

4. may be positive or may be negative

Q.

The physical quantity having the dimensions $\left[M^{-1}{L}^{-3}{T}^3{A}^2\right]$ is

1. resistance

2. resistivity

3. electrical conductivity

4. electromotive force

Q.

List three sources of magnetic fields.

Q. Nickel shows ferromagnetic property at room temperature. If the temperature is increased beyond Curie temperature, then it will show

1. anti ferromagnetism
2. no magnetic property
3. diamagnetism
4. paramagnetism

Q. Conductivity of metal decreases with temperature while conductivity of electrolytic conductors increases with temperature. Why ?

Q.

Write two properties of a material suitable for making (a) a permanent magnet, and (b) an electromagnet

Q. I-V graph for a mettallic wire at two different temperatures, $T_1$ and $T_2$ is as shown in the figure.

Which of the two temperature is lower and why?

Q.

Among silver and copper, which one is a better conductor and why?

Q. The most suitable metal for permanent magnets is

1. Steel
2. Iron
3. Copper
4. Aluminium

Q. The magnetization curve for a ferromagnetic material is shown in the diagram. The value of relative permeability is highest at point,

1. $\text{P}$
2. $\text{Q}$
3. $\text{R}$
4. Data insufficient

Q. ${\mu }_e$ and ${\mu }_h$ are the electron and hole mobilities of a semiconducting crystal respectively. $E$ is the applied electric field. Then the current density $J$ for the intrinsic semiconductor is (Take $n_i$ the intrinsic concentration of the semiconductor)-

1. $n_{i}e({\mu }_e+{\mu }_h)E$
2. $n_{i}e({\mu }_e-{\mu }_h)E$
3. $\frac{n_{i}e({\mu }_e+{\mu }_h)}{E}$
4. $\frac{E}{n_{i}e({\mu }_e+{\mu }_h)}$

Q. If a copper wire is stretched to make it $0.1\%$ longer, the percentage increase in resistance will be

1. 0.2
2. 2
3. 1
4. 0.1

Q.

Why does magnetic field increases the resistivity of all metals except iron , cobalt and nickel ?

Q.

How does the short circuit form? What is its effect?

Q. A thin bar magnet is cut into two equal parts . The ratio of moment of inertia to the magnetic moment of each part will become

Q. Write two properties of a material suitable for making (a) a permanent magnet, and (b) an electromagnet.

Q. A wire has a resistance of $3\Omega$ at ${40}^{\circ }$C and resistance of $5\Omega$ at ${100}^{\circ }$C. The temperature coefficient of resistance of the wire is

1. ${0.0012}^{\circ }{C}^{-1}$
2. ${0.0222}^{\circ }{C}^{-1}$
3. ${0.0024}^{\circ }{C}^{-1}$
4. ${0.0111}^{\circ }{C}^{-1}$

Q.

What is the main parameter to distinguishing two types of magnetic materials namely Soft And Hard?

Q. The electrical resistance of a conductor depends upon.

1. Temperature of conductor
2. Size of conductor
3. Geometry of conductor
4. All of these

Q. Can superconductors exhibit resonance ? Why or why not ?

Q. Assertion :The kinetic energy of electrons in a metallic wire will increase, if the temperature of the wire is increased. Reason: On increasing temperature, conductivity of metallic wire decreases.

1. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
2. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
3. Assertion is correct but Reason is incorrect
4. Assertion is incorrect but Reason is correct

Q.

Who invented the semiconductor?

Q. The resistance of a semiconductor material (germanium or silicon)_______ with rise in temperature.

1. remains the same
2. decreases
3. increases
4. first increases then decreases

Q.

Describe the working of paramagnetism.

Q. The resistivity of a semiconductor

1. Remains constant even when temperature varies
2. Decreases as the temperature increases
3. None of the above
4. Increases as the temperature increases