RP4 - 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 meters 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 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 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 through 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

WILL BE WRITTEN ON PAPER:

What would you expect the I-V graph of a resistor to look like?

Answer 10

I is Directly Proportional to V. So staight horizontal line in the middle of I and V

Question 11

WILL BE WRITTEN ON PAPER:

What would you expect the I-V graph of a diode to look like?

Answer 11

The line would be horizontal across the x axis in the I-V graph but ventually it will have a sudden rise in the upper right quart.

Question 12

WILL BE WRITTEN ON PAPER:

What would you expect the I-V graph of a lamp to look like?

Answer 12

In the I-V graph it will be and S like shape.

Question 13

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

Answer 13

● Resistance increases
● Ions 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