Question

The value of critical current density in a superconductor depends upon

1. temperature

2. magnetic field strength

3. penetration depth

Which of the above are correct?
1. 1, 2 and 3
2. 1 and 3 only
3. 2 and 3 only
4. 1 and 2 only

Answer 1

Correct Answer - Option 4 : 1 and 2 only

The Silsbee effect states that, if the current exceeds a critical level, the superconducting state will be destroyed.

Critical current is mathematically defined as:

I_C = 2πr H_c

r = radius of superconductor wire

H_c = critical magnetic field strength

Critical current density will be the ratio of the critical current to the area, i.e.

\({J_c} = \frac{{{I_c}}}{A}\) 

\({J_c} = \frac{{2\pi r\;{H_c}}}{A}\) 

\({J_c} = \frac{{2\pi r\;\;{H_0}\left[ {1 - {{\left( {\frac{T}{{{T_c}}}} \right)}^2}} \right]}}{A}\) 

Observations: From the above equation, we observe that the critical current density depends only on both the temperature and magnetic field strength.

Superconductivity: It is the state of the material in which its resistance becomes zero as well as it behaves as perfect diamagnetic when its temperature is reduced below transition temperature Tc and the magnetic field is less than the critical magnetic field Hc.

∴  The current density of the superconductor depends on critical magnetic field strength and temperature.