7.3 Resistance

Question 1

What is resistance?

Answer 1

Resistance is anything in a circuit that reduces the flow of current.

The greater the resistance in a circuit, the smaller the current that can flow through it

Question 2

What is the unit of resistance?

Answer 2

Ohms (Ω)

Question 3

What equiation relates potential difference, current and resistance?

Answer 3

V = I x R

V = potential difference (in volts, V)

I = current (in amperes, A)

R = resistnace (in ohms, Ω)

Question 4

HOw is resistance related to temperature?

Answer 4

As temperature increases, resistance increases

Question 5

Explain the relationship between temperature and resistance in metals.

Answer 5

In metals, electrical current is due to the flow of electrons through a lattice of metal ions

As electrons collide with ions, some energy is transferred to the ions, heating them up

Hotter ions vibrate more, and so have fewer gaps between them for the electrons to flow through

The more ions vibrate (i.e. when they are hotter), the more electrons collide with the ions as they flow through the lattice - this creates more resistance and lessens the flow of current

Eventually, when the metal is hot enough, no electrons can get through, so no electricity will flow