Required practical 4 - I-V characteristics

Question 1

Outline the basic steps of the practical

Answer 1

1) Set up circuit with lamp/resistor/diode.
2) Alter the potential difference in regular increments.
3) Record the current for each potential difference.
4) Plot a graph of current against potential difference.
5) Repeat for the other 2 components.

Question 2

What 2 types of meters are needed in the circuit, and how should they be connected?

Answer 2

Voltmeter - connected in parallel to the component.

Ammeter - connected in series with the component.

Question 3

What component is required to alter potential difference if you’re not using a variable power pack?

Answer 3

A rheostat, or variable resistor

Question 4

What is an ‘ohmic conductor’? State the condition required

Answer 4

• A conductor for which current and potential difference are directly proportional.
• Resistance remains constant as current changes.
• Temperature must be constant.

Question 5

What specific type of ammeter may be required in this experiment and why?

Answer 5

A milliammeter since the currents and current changes involved may be quite low.

Question 6

What must also be present in the circuit when the diode test is being tested? Where should it be connected?

Answer 6

A protective resistor should be connected to prevent the current levels getting too high. It should be connected in series with the diode.

Question 7

For which component does the polarity of the power supply matter and why?

Answer 7

The diode, since diodes only allow current to flow in one direction.

Question 8

What must be kept constant to get reliable results? How can you achieve this?

Answer 8

Temperature should remain constant so that the resistance of the components isn’t affected. You should disconnect the supply when not taking readings to avoid unnecessary heating.

Question 9

How do you determine the resistance of a component from an I-V graph?

Answer 9

The resistance at a given point, is the inverse of the gradient of the line drawn from that point to the origin.
Work out the gradient and use 1/gradient to obtain the resistance.

Question 10

What happens to the resistance of a filament lamp as the temperature increases?

Answer 10

• Resistance increases.
• Ions in metal have more energy, so vibrate ore energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow.