# Engineering Physics Questions and Answers – Hall Effect

This set of Engineering Physics Interview Questions and Answers for freshers focuses on “Hall Effect”.

1. When does a normal conductor become a superconductor?
a) At normal temperature
b) At Curie temperature
c) At critical temperature
d) Never

Explanation: The temperature at which a normal conductor loses its resistivity and becomes a superconductor is known as transition temperature or critical temperature.

2. In which of the following does the residual resistivity exist?
a) Impure metal at high temperature
b) Pure metal at low temperature
c) Pure metal at high temperature
d) Impure metal at low temperature

Explanation: When the temperature is reduced to 0K, the resistivity of the impure metal doesn’t become zero, because there exist some impurities which gives rise to minimum resistivity known as residual resistivity.

3. Meissner effect occurs in superconductors due to which of the following properties?
a) Diamagnetic property
b) Magnetic property
c) Paramagnetic property
d) Ferromagnetic property

Explanation: A diamagnetic material has a tendency to expel magnetic lines of forces. Since the superconductor also expels magnetic lines of force it behaves as a perfect diamagnet. This behaviour is first observed by Meissner and is hence called Meissner effect.

4. What happens when a large value a.c. current is passed through superconductors?
a) Conductivity increases
b) Superconducting property is destroyed
c) It acts as a magnet
d) It becomes resistant

Explanation: When a large value of a.c. current is applied to a superconducting material it induces some magnetic field in the material and because of this magnetic field, the superconducting property of the material is destroyed.

5. How is persistent current produced in supermagnets?
a) By passing ac current
b) By magnetising it
c) By passing dc current
d) By increasing the resistance

Explanation: When dc current of large magnitude is once induced in a super conducting ring then the current persists in the ring even after the removal of the field. This current is called persistent current. This is due to diamagnetic property. The magnetic flux inside the ring will be trapped in it and hence current persists.

6. Superconductors can be used as a memory or storage elements in computers.
a) True
b) False

Explanation: Since the current in superconducting ring can flow without any change in its value, it can be used as a memory or storage element in computers.

7. Superconducting tin has a critical temperature of 3.7K at zero magnetic field and a critical field at 0.0306 Tesla at 0K. Find the critical field at 2K.
a) 0.0306 Tesla
b) 7.4 Tesla
c) 0.02166 Tesla
d) 0 Tesla

Explanation: Critical field, Hc = H0 [1-T2/(Tc)2)]
Critical college = 0.02166 Tesla.

8. Calculate the critical current for a wire of lead having a diameter of 1mm at 4.2 K. Calculate temperature for lead is 7.18 K and Hc = 6.5×104 A/m. Critical field is 42.758×103 A/m.
a) 3.5593 A
b) 27.3 A
c) 46.67 A
d) 134.26 A

Explanation: Critical current Ic = 2πrHc
Ic = 134.26 A.

Sanfoundry Global Education & Learning Series – Engineering Physics.