Required Practical: Investigating IV Characteristics

Question 1

Describe the method for investigating how the voltage across a component affects the current through it. (5)

Answer 1

1. Set a circuit so that an ammeter, variable resistor, and lamp are in series with the battery, and the voltmeter is in parallel with the lamp.
2. Measure the p.d. on the voltmeter and current on the ammeter.
3. Change the resistance of the variable resistor and repeat step 2.
4. Repeat steps 2 and 3 for a range of p.d.’s and currents.
5. Plot a graph of p.d. on the x-axis and current on the y-axis.

Question 2

Suggest and explain a way of improving the accuracy of investigating IV characteristics. (3)

Answer 2

• The switch should be used with the resistor.
• This avoids the issue of the current, causing a heating effect in the resistor.
• If the temperature of the resistor increases, the resistance of the resistor will increase.

Question 3

Describe the results of investigating IV characteristics.

Answer 3

• The current is directly proportional to the potential difference for a resistor.
• This relationship is called Ohms law and any component that demonstrates this relationship is called an ohmic component.

Question 4

What is Ohm’s law for a resistor?

Answer 4

•The current is directly proportional to the potential difference
• As the temperature is constant

Question 5

What does a straight line on an IV characteristics of a variable resistor tell us?

Answer 5

That the resistance is constant.

Question 6

What does a curve on a graph showing IV characteristics of a filament lamp tell us? (2)

Answer 6

• As the current increases, the temperature of the wire increases.
• This causes the resistance of the filament in the bulb to increase.

Question 7

What does a graph showing IV characteristics of a diode tell us?

Answer 7

• A diode will only allow a current to pass through it in one particular direction once the p.d. has reached a certain value.
• At p.d.’s below this, the resistance of the diode is very big.

Question 8

What are LDRs and thermistors? (3)

Answer 8

• LDRs and thermistors are special resistors whose existence depends on external factors.
• LDRs can be used to detect changes in light intensity such as street lighting or security.
• Thermistors can be used in temperature control devices.

Question 9

Describe how light intensity affects LDRs.

Answer 9

As the light intensity that the LDR is exposed to increases, the resistance of the LDR decreases.

Question 10

Describe how temperature affects the resistance of a thermistor.

Answer 10

As the temperature of the thermistor increases, the resistance decreases.