RP3: Investigating IV characteristics (how the voltage affects the current)

Question 1

Equipment (7p)

Answer 1

• a cell
• ammeter
  -voltmeter
  -crocodile clips
• 2 100 Ω resistors
• 1 50 Ω resistor
• connecting leads

Question 2

Method (6p)

Answer 2

1) Set up circuit as shown in diagram
2) Measure the p.d. on the voltmeter and the current on the ammeter
3) Change the resistance of the variable resistor and repeat step 2
4) Repeat step 2 and 3 for a range of p.d. and current
5) Reverse the connection to the cell (so the p.d. and current are negative) and repeat steps 2 and 4
6) plot a graph with p.d. on the x axis and current on the y axis

Question 3

Way to make the experiment more accurate (2p)

Answer 3

• Use a switch with the resistor
• This makes sure the current doesn’t heat up the resistor, therefore increasing the resistance

Question 4

Ohms law for a resistor

Answer 4

• the current is directly proportional to the p.d. as long as the temperature of the resistor is constant

Question 5

What are IV characteristics?

Answer 5

Graphical representations showing the relationship between the current flowing through a component and the voltage applied across it.

Question 6

IV characteristics of a resistor (3p)

Answer 6

• current is directly proportional to p.d.
• this means that the resistance is constant as the current changes
• shown as a straight line on a graph

Question 7

IV characteristics of a filament lamp (3p)

Answer 7

• as the current increases, the temperature of the wire increases
• this causes the resistance of the filament in the bulb to increase
• shown as a curve on a graph

Question 8

IV characteristics of a diode/LED (3p)

Answer 8

• A diode will only allow current to pass through it in one particular direction once the p.d. has reached a certain level
• At p.d. ‘s below this, the resistance is very big
• Shown on graph as a flat line on x axis until the p.d. has been reached; then it’s a upwards line