9.4 Resistance

Question 1

What is resistance defined as?

Answer 1

The resistance of a component is defined as the ratio between the potential difference across a component and the current flowing through it:

R= V/ I
1 Ω= 1 V A^-1= 1kg m^2 s^-3 A^-2

Question 2

What is Ohm’s law?

Answer 2

For a metallic conductor at constant temperature the potential difference across the conductor is directly proportional to the current flowing through the conductor:
V= IR
1V = 1AΩ = 1kg m^2 s^-3 A^-1

Question 3

Why does the current in a wire decrease over time?

Answer 3

Over time, the wire becomes hotter as thermal energy is transferred to it by the charge carriers. This makes the positive ions in the wire vibrate more frequently, making it harder for the charge carriers to flow through thus increasing resistance. Voltage stays the same throughout.

Question 4

How does temperature affect resistance in a wire?

Answer 4

The hotter a metal gets, the greater the resistance to the flow of current it has. This is because positive ions transfer thermal energy into kinetic energy, vibrating more frequently and violently, making it harder for the charge carriers to pass through.