Req Prac 3 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 p.d
4. Plot a graph of current against p.d
5. Repeat for the other two components

Question 2

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

Answer 2

1. Voltmeter: connected in parallel to the component
2. 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 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 doide

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 ?Why ?

Answer 10

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