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

Answer 2

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

Question 2

what must also be present in the circuit when the diode is being tested? where should it be connected?

Answer 2

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

Question 2

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

Answer 2

1. voltmeter: connecteed in parallel to the component
2. ammeter: connected in series with the component

Question 2

what is an ‘ohmic conductor’? state the condition required.

Answer 2

• a conductor for which current and potential difference and directly proportional
• resistance remains constant as current changes
• temperature must be constant

Question 2

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

Answer 2

• 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

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 3

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

Answer 3

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 gradiant and use 1/gradient to obtain the resistance.

Question 4

what must be kept constant to get reliable results? how can you achieve this?

Answer 4

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 4

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

Answer 4

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