Chpt 23 - Resistance

Question 1

What is resistance?

Answer 1

(of a conductor) is the ratio of the p.d. across it to the current flowing through it. (R = V/I)
–> Unit = Ohm

Question 2

What is ohm’s law?

Answer 2

For certain conductors (mainly metals), at constant temperature, the current flowing through them is directly proportional to the p.d. across them ( V & I –> V/I = a constant)

Question 3

Resistors in series

Answer 3

(R = R1 +R2 + R3)

Question 4

Resistors in parallel

Answer 4

(1/R = 1/R1 +1/R2 + 1/R3)

Question 5

Factors affecting the resistance of a conductor:

Answer 5

Temperature
length
Cross-sectional Area
Material (from which its made)

Question 6

What is a thermistor?

Answer 6

a semiconductor whose resistance decreases rapidly with increasing temperature.

Question 7

What is resistivity?

Answer 7

p (rho) = RA/l
unit = Ohm metre