3.4 V=IR Equation & I-V Graphs

Question 1

What is the equation that links potential difference, current and resistance?

Answer 1

Potential difference (V) = current (A) x resistance (Ohms)

Question 2

If the resistance of a circuit is low, would the resistance graph show a steep or less steep line?

Answer 2

Steep

Question 3

Which two components would be used in a circuit to measure resistance and how?

Answer 3

• Ammeter: this measures the current (in amps) flowing through the test wire. It can be put anywhere in the main circuit - but it must be placed in series with the test wire, never in parallel.
• Voltmeter: this measures the potential different across the test wire (in volts). It must be placed in parallel with the wire, not any other bit of the wire.

Question 4

What are filament lamps?

Answer 4

Lamps that contain a very thin metal filament

Question 5

What do diodes do?

Answer 5

They only allow current to flow in one direction, which is why they only show a current on a graph when the potential difference is positive.

Question 6

Why does increasing the temperature of a circuit increase resistance?

Answer 6

As temperature increases, all of the ions in the metal vibrate faster, which makes it harder for electrons to pass along the wire.

Question 7

What does the term ‘I-V characteristics’ refer to?

Answer 7

A graph which shows how the current (I) flowing through a component changes as the potential difference (V) is increased

Question 8

What type of resistance do linear components have?

Answer 8

A constant resistance

Question 9

What type of I-V characteristic graph do non-linear components have?

Answer 9

A curved graph

Question 10

Describe what the resistance of a thermistor is dependent on

Answer 10

The resistance of a thermistor is dependent on its temperature - as the current increases, the thermistor warms up so the resistance decreases, which is why it has a curved I-V characteristic.