Required Practical Activity 4

Question 1

Circuit diagram to find I-V characteristics of filament lamp:

Answer 1

Question 2

Method to find I-V characteristics of filament lamp:

Answer 2

1. Set up apparatus as shown in circuit diagram above
2. Change reading on variable resistor until potential difference across filament bulb is -10V (measure the potential difference across the filament bulb using the voltmeter)
3. Measure current using ammeter connected in series to circuit while potential difference across bulb is -10V
4. Repeat the experiment but continue to change the reading on the variable resistor until potential difference on voltmeter across the filament bulb in increments of 1V up to 10V
5. Plot graph of results with potential difference on x-axis and current on the y-axis

Question 3

Graph of current and potential difference of a filament lamp:

Answer 3

Question 4

How do you improve the accuracy when finding the I-V characteristics of a filament bulb?

Answer 4

• Use the same components for each repeat
• Do not just use the same value of component as they may be slightly different from one another
• Use a low currentand turn the circuit off between readings - this prevents the wires and components increasing in temperature which would increase resistance and affect future readings including repeat readings

Question 5

What are the results for the I-V characteristics of a filament bulb?

Answer 5

• As potential difference increases, current increases
• At small potential differences the relationship between potential difference and current is linear (the gradient is constant)
• At large potential differences the gradient becomes more shallow as the resistance of the bulb increases due to a higher temperature in the circuit

Question 6

Explain the results for the I-V characteristics of a filament bulb:

Answer 6

• At small potential differences there is a small current so the heating effect of the current is small and the filament remains at a low temperature
• At large potential differences there is a large electrical current so the heating effect of the current is large which causes the filament to be a high temperature
  
  • This is caused by electrons in the wire colliding with ions in the metal lattice causing them to vibrate
• Wires (like the filament) have a greater resistance at higher temperatures, causing the increase in current to be reduced
• This is because the more the ions in the metal lattice vibrate the more likely electrons are to collide with
  them and slow down

Question 7

Circuit diagram to find I-V characteristics of a diode:

Answer 7

Question 8

Method to find I-V characteristics of a diode:

Answer 8

1. Set up apparatus as shown in circuit diagram above
2. Change reading on variable resistor until potential difference across diode is -10V (measure the potential difference across the diode using the voltmeter)
3. Measure current using ammeter connected in series to circuit while potential difference across diode is -10V
4. Repeat the experiment but continue to change the reading on the variable resistor until potential difference on voltmeter across the diode in increments of 1V up to 10V
5. Plot graph of results with potential difference on x-axis and current on the y-axis

Question 9

Graph of current and potential difference of a diode:

Answer 9

Question 10

How do you improve the accuracy when finding the I-V characteristics of a diode?

Answer 10

• Use the same components for each repeat
• Do not just use the same value of component as they may be slightly different from one another
• Use a low current and turn the circuit off between readings
• This prevents the wires and components increasing in temperature which would increase resistance and affect future readings including repeat readings

Question 11

What are the results for the I-V characteristics of a diode?

Answer 11

• For a positive potential difference the current increases rapidly with an increase in potential difference
• For a negative potential differencethe current remains negligible and does not increase as the potential difference becomes larger

Question 12

What is the explanation behind the I-V characteristics of a diode?

Answer 12

The resistance of a diode is very low for current in the forward direction and very high in the back direction

Question 13

Circuit diagram to find I-V characteristics of a resistor:

Answer 13

Question 14

Method to find IV characteristics of a resistor:

Answer 14

1. Set up apparatus as shown in circuit diagram above
2. Change reading on variable resistor until potential difference across diode is -10V (measure the potential difference across the resistor using the voltmeter)
3. Measure current using ammeter connected in series to circuit while potential difference across the resistor is -10V

(reverse the polarity of an electrical circuit, you can switch the connections of the positive and negative terminals of the power supply or battery)

4. Repeat the experiment but continue to change the reading on the variable resistor until potential difference on voltmeter across the resistor in increments of 1V up to 10V
5. Plot graph of results with potential difference on x-axis and current on the y-axis

Question 15

Graph of current and potential difference across a resistor:

Answer 15

Question 16

How do you improve the accuracy when finding the I-V characteristics of a resistor?

Answer 16

• Use the same components for each repeat
• Do not just use the same value of component as they may be slightly different from one another
• Use a low current and turn the circuit off between readings
• This prevents the wires and components increasing in temperature which would increase resistance and affect future readings including repeat readings

Question 17

What are the results for the I-V characteristics of a resistor?

Answer 17

• As potential difference increases, current increases
• The relationship between potential difference and current is linear (the gradient is constant)
• The current is directly proportional to potential difference

Question 18

What is the explanation behind the I-V characteristics of a resistor?

Answer 18

Resistors obey Ohm’s Law so the “current through a resistor at constant temperature is directly proportional to the potential difference across the resistor”