Required practical 4 - I-V characteristics

Question 1

what is the aim of the experiment?

Answer 1

to investigate the relationship between current and potential difference for a resistor, bulb and diode

Question 2

what are I-V characteristics?

Answer 2

how the current varies as you change the potential difference across a component

Question 3

how would you conduct the experiment? (resistor + filament bulb)

Answer 3

1. connect a circuit containing: a power supply, a variable resistor, an ammeter, a voltmeter and a fixed resistor
2. ensure power supply is set to 0 at the start
3. record the reading on the voltmeter and ammeter
4. use the variable resistor to increase pd to 1V
5. record the new readings on the voltmeter and ammeter
6. repeat steps 4 and 5 but increase pd by 1 each time
7. reverse power supply connections and repeat everything so far
8. repeat the entire experiment with a bulb
9. plot a graph of current against potential difference for each component

Question 4

what does the graph for a fixed resistor look like?

Answer 4

• x-axis = pd
• y-axis = current
• it is a straight line that goes through the origin

Question 5

what can you conclude about a resistor’s I-V characteristics?

Answer 5

potential difference is directly proportional to current - it follows Ohms Law because a resistor is an ohmic conductor

Question 6

what does the graph for a filament bub look like?

Answer 6

• x-axis = pd
• y-axis = current
• it is a curved graph with the parts closest to the origin steepest and the curve being much flatter at the extremes

Question 7

what can you conclude about a filament bulb’s I-V characteristics?

Answer 7

• current doesn’t increase as fast as potential difference
• the more energy that is put into the bulb, the more the resistance of the bulb increase
• as pd increases, temperature of the filament increases, vibrations of ions in the filament increase, so it is harder for electrons to get past

Question 8

how do you conduct this experiment? (semiconductor diode)

Answer 8

1. connect the circuit with a power supply, a variable resistor, an ammeter, a voltmeter, a diode and a protective resistor (between 100-500Ω)
2. set the variable resistor to give that lowest potential difference of 0.2V and record the readings on the voltmeter and ammeter
3. alter the variable resistance to increase pd by 0.2V
4. record new readings on the voltmeter + ammeter
5. repeat steps 3 and 4 each time increasing pd by 0.2V
6. reverse power supply connections and repeat steps 2-6
7. plot a graph of current against pd for the diode

Question 9

what does the graph for the diode look like?

Answer 9

• x-axis = pd
• y-axis = current
• it looks like a deathslide - it stays at 0 on the negative side and then shoots up on the positive side

Question 10

what can you conclude about the diode’s I-V characteristics?

Answer 10

• current only flows through the diode if it is flowing forwards
• when current is flowing forward the diode’s resistance is large at low pds but at higher pds resistance quickly drops and current begins to flow

Question 11

what are the hazards associated with this experiment and how are they managed?

Answer 11

• heating of resistor - burns to skin - don’t touch it while circuits are connected and allow time to cool