Answer to Question #305203 in Electric Circuits for Shane

Question

1. How would you expect the resistivity of a good insulator such as glass or polystyrene to vary with temperature?

2. A fuse is a device that is designed to break the circuit. It melts when the current exceeds its value. What

characteristics should the material have?

1. Find the current density and drift velocity of free electrons when the particles travel on a copper conductor with a

square cross-section of 1.0 mm on the side and carries a current of 40 A to a 5 hp electric meter and its density of

6.0 x 1028 electrons/m3

2. Suppose the resistance is 1.47 Ω at a temperature of 20°C. Find the resistance at 0 degree Celsius.

Answer 1

Solution;

1.

Resistance will decrease with increasing temperature. This is mainly due to the large energy gap between the different bands.

2.

The material should have low melting point and high resistivity

3.

Current density;

$J=\frac{I}{A}$

$J=\frac{40}{1×10^{-6}}=40×10^6A/m^2$

Drift velocity;

$V_d=\frac{I}{\mu eA}$

$V_d=\frac{40}{6×10^{28}×1.6×10^{-19}×1×10^{-6}}$

$V_d=4.1667×10^{-3}m/s$