Circuit investigations

Question 1

Why do we repeat readings

Answer 1

We repeat readings to find any anomalous results

Question 2

Why do we calculate an average

Answer 2

We calculate an average from our repeated readings to eliminate the effect of random errors

Question 3

Draw the circuit diagram for investigating current and voltage for a resistor

Answer 3

Include
Variable Power supply
Ammeter
Resistor
Voltmeter connected to the resistor in parallel
Switch

Question 4

State the method for investigating current and voltage for a resistor

Answer 4

With the power supply off, set up the circuit
Increase the voltage, close the switch and record readings from the ammeter and voltmeter
Repeat this method, for higher voltages
Swap the connections of the power supply and repeat the whole experiment for negative values of current and voltage

Question 5

Draw the graph for investigating current and voltage for a resistor

Answer 5

Straight line passing through the 1st quadrant and the 3rd quadrant
Voltage - on x-axis
Current - on y-axis

Question 6

Using the graph, a conclusion for investigating current and voltage for a resistor

Answer 6

The graph is a straight line through the origin, therefore the current is directly proportional to the voltage (Current ∝ Voltage) - (as voltage doubles, current doubles)

This applies to both positive and negative values of voltage and current

This is true if resistance is constant
This is true for a resistor (and any conductor if its temperature is constant

Question 7

Use the graph for investigating current and voltage for a resistor, to calculate resistance

Voltage = 10V
Current = 2.3A

Answer 7

E.g.
Go up from 10V until you hit the line - 2.3A
Voltage = 10V
Current = 2.3A
When voltage is 10, current is 2.3

Gradient = ∆y/∆x = 2.3/10 = 0.23 = I/V
Resistance = V/I = 1/gradient = 1/0.23 = 4.3Ω (to 1 d.p.)

Question 8

Draw the circuit diagram for investigating the current and voltage for a diode

Answer 8

See book

Question 9

Using a diode, how do you know which direction in which the current flows

Answer 9

The direction of the arrow of a diode represents the direction in which the current moves

Question 10

State the method for investigating the current and voltage for a diode

Answer 10

Using the Potential divider, vary the voltage that the diode recieves

As the voltage is increased, record readings from the ammeter and voltmeter
To obtain negative values of current and voltage, swap the connections of the power supply

Question 11

Draw the graph for investigating the current and voltage for a diode

Answer 11

Graph showing 1st and 2nd quadrants
https://bam.files.bbci.co.uk/bam/live/content/zwmb7p3/large

Question 11

Draw the graph for investigating the current and voltage for a diode

Answer 11

Graph showing 1st and 2nd quadrants
https://bam.files.bbci.co.uk/bam/live/content/zwmb7p3/large

Question 12

Using the graph write a conclusion for investigating the current and voltage for a diode

Answer 12

A diode only allows current to flow in one direction.
If the potential difference is arranged to try and push the current the wrong way (also called reverse-bias) no current will flow as the diode’s resistance remains very large.
Current will only flow if the diode is forward-biased.
When forward-biased, the diode’s resistance is very large at low potential differences but at higher potential differences, the resistance quickly drops and current begins to flow.

Question 13

What is the threshold voltage - in terms of for investigating the current and voltage for a diode

Answer 13

The threshold voltage is the voltage when the current starts to flow

Question 14

Name the graph with a straight line through the origin

Answer 14

The current-potential difference graphs for a resistor at constant temperature

Question 15

Name the graph that curves - identify the component this relates with

Answer 15

Filament lamp

Question 16

Name the graph where current is 0, then increases rapidly - identify the component this relates with

Answer 16

Diode

Question 17

Describe the resistance of an LDR in the dark

Answer 17

In the dark, a LDR has a very high resistance

Question 18

Describe the resistance of an LDR in light

Answer 18

In light, the LDR has a very low resistance

Question 19

What is the LDR used for

Answer 19

The LDR is used as a light sensor

Question 20

Describe the resistance of a thermistor when it is cold

Answer 20

When it is cold, the thermistor has a very high resistance

Question 21

Describe the resistance of a thermistor when it is hot

Answer 21

When a thermistor is hot, it has a very low resistance

Question 22

What are thermistors used for

Answer 22

Thermistors are used as a temperature sensor

Question 23

Draw the symbols for:
switch (open)
switch(closed)
cell
battery
Diode
Resistor
Variable resistor
Lamp
Fuse
Voltmeter
Ammeter
Thermistor
LDR
LED

Answer 23

https://bam.files.bbci.co.uk/bam/live/content/z3cxgdm/large

Question 24

Draw the circuit diagram for an automatic lighting circuit/system

Answer 24

Includes
Battery, LDR, Variable resistor, A bulb connected in parallel to the LDR

Question 25

Explain how the automatic lighting circuit/system works

Answer 25

When it is light, the resistance of the light dependent resistor is low, therefore the voltage across it is also low

The bulb in parallel, with the light dependent resistor, receives the same voltage, and is therefore off.

When it is dark, the resistance of the LDR is very high, it therefore receives a much higher voltage, the bulb receives the same voltage and switches on

The variable resistor controls the sensitivity of the circuit, if it’s resistance is high, then it must be much darker for the light to switch on