## Electric - charge and current

Where needed take the charge on the electron to be –1.6x10

1. Why does the resistance of a metal increase with temperature?

2. (a) What is meant by free electrons?

(b) how are they moving within a solid?

3. Why does an insulator not conduct electricity?

4. What would you have to do to a sample of semiconductor to decrease its resistance? Explain your answer.

5. What is the approximate drift velocity of a ‘cloud’ of free electron through the bulb in a torch?

6. Express the following in AMPS:

(a) 2mA

(b) 5μA

(c) 6MA

(d) 12pA

(e) 10

7. How could the drift velocity of electons be increased?

8. Draw a diagram of a Thermionic diode and explain how the number of electrons crossing the tube varies with the applied voltage.

9. Calculate the charge passing a point in a wire when the following currents flow in a wire for the times given:

(a) 25mA 20s

(b) 3A 5m

(c) 10 μA 5 weeks

10. Calculate the current in a wire when the following charges flow past in the times given:

(a) 20 C in 5s

(b) 0.5 C in 25

(c) 10

(d) 12 C in 2 minutes

^{-19}C1. Why does the resistance of a metal increase with temperature?

2. (a) What is meant by free electrons?

(b) how are they moving within a solid?

3. Why does an insulator not conduct electricity?

4. What would you have to do to a sample of semiconductor to decrease its resistance? Explain your answer.

5. What is the approximate drift velocity of a ‘cloud’ of free electron through the bulb in a torch?

6. Express the following in AMPS:

(a) 2mA

(b) 5μA

(c) 6MA

(d) 12pA

(e) 10

^{2}mA7. How could the drift velocity of electons be increased?

8. Draw a diagram of a Thermionic diode and explain how the number of electrons crossing the tube varies with the applied voltage.

9. Calculate the charge passing a point in a wire when the following currents flow in a wire for the times given:

(a) 25mA 20s

(b) 3A 5m

(c) 10 μA 5 weeks

10. Calculate the current in a wire when the following charges flow past in the times given:

(a) 20 C in 5s

(b) 0.5 C in 25

(c) 10

^{15}electrons in 2s(d) 12 C in 2 minutes