physics help

Question

4.1. the field coils of motor have a resistance of 50 ohms at 10 degrees Celsius. After a run at full load, the resistance increases to 100 ohms and the temperature of the coils to 201 degrees Celsius. Calculate the temperature coefficient of resistance at 0 degrees Celsius. 4.2. the field-coil of motor has a resistance of 100 ohms at 15 degrees Celsius. By how much will the resistance increase if the motor reaches a temperature of 65 degrees Celsius when running? Take the temperature coefficient of resistance to be 0,004 per degrees Celsius at 15 degrees Celsius. 4.3. difference between positive and negative coefficient of resistance.

Answer 1

Step 1:

(4.1)

The resistance of the field coil of motor at 10° C is 50 .

The resistance of the field coil of motor at 201° C is 100 .

Find temperature coefficient at 0° C.

Temperature coefficient at 0° C : .

Temperature coefficient at 0° C is /C.

Solution:

Temperature coefficient at 0° C is /C.

Answer 2

Step 1:

(4.2)

The resistance of the motor at 15° C is 100 .

Temperature coefficient is 0.004/C.

Final temperature is 65° C

Find the increase in resistance.

Temperature coefficient at 0° C : .

The increase in resistance is 20 .

Solution:

The increase in resistance is 20 .

Answer 3

Step 1:

(4.3)

Negative coefficient of resistance :

The resistance of the material decreases with increase in temperature,this phenomenon is said to be negative temperature coefficient of semiconductor.

Semiconductors and insulators have negative temperature coefficient. These are used as thermistors.

Positive coefficient of resistance :

The resistance of the material increases with increase in temperature,this phenomenon is said to be positive temperature coefficient of semiconductor.

Usually all metals and their alloys have positive temperature coefficient.

Solution:

The difference between between Negative coefficient of resistance and positive coefficient of resistance is the resistance of the material.