Electricity - Current, Potential Difference, And Resistance

Question 1

Copy this link to test understanding of circuit components.

Answer 1

https://cdn.savemyexams.com/cdn-cgi/image/f=auto,width=1200/https://cdn.savemyexams.com/uploads/2021/07/2.1.1-Circuit-Symbols-GCSE.png

Question 2

What is a cell/battery?

Answer 2

A cell provides a circuit with a source of potential difference, a battery is 2 or more cells.

Question 3

What is a switch?

Answer 3

Turns the circuit on (closed) or off (open).

Question 4

What is a fixed/variable resistor?

Answer 4

A fixed resistor has a resistance it cannot change, a variable has a slider that can change the resistance.

Question 5

What is a thermistor?

Answer 5

The resistance of this resistor depends on its temperature, as its temperature increases, its resistance decreases.

Question 6

What is a light-dependent resistor?

Answer 6

The resistance of an LDR depends on the light intensity. As light intensity increases, resistance decreases.

Question 7

What is a diode?

Answer 7

A diode allows current to flow in one direction only, current flows through the diode when it is in forward bias position.

Question 8

What is a light emitting diode?

Answer 8

A diode that emits light when current passes through it.

Question 9

What is a fuse?

Answer 9

A device designed to cut of the flow of current if the current is too large.

Question 10

What is an ammeter/voltmeter?

Answer 10

An ammeter measures current, connected in series, a voltmeter measures volts, connected in parallel.

Question 11

What 3 things are needed for a circuit diagram?

Answer 11

1. Energy source
2. A closed circuit
3. Electrical components

Question 12

What does electrical charge need to flow?

Answer 12

It needs a potential difference across the circuit.

Question 13

What is potential difference defined as?

Answer 13

The energy transferred per unit of charge flowing from one point to another.

Question 14

How is potential difference calculated by the energy of charge?

Answer 14

Potential difference = Work done or energy/ Charge

V = W or E / Q

Question 15

What is electrical current?

Answer 15

The flow of electric charge.

Question 16

How is charge calculated?

Answer 16

Charge = Current*time
Q = It

Question 17

What is resistance?

Answer 17

The opposition to current.

This means the factors the cause electrons to transfer energy slowing them down (e.g the vibrations of atoms in the wire).

Question 18

How can potential difference be calculated by resistance?

Answer 18

Potential difference = current*resistance

V = IR

Question 19

How would we investigate how resistance changes as the length of a wire increases?

Answer 19

1. Get a power pack and create a circuit using a wire, get a 10cm wire and connect a crocodile clip to each end.
2. Connect the wire, using the clips, to the rest of the circuit.
3. Connect an ammeter in series with the 10cm wire and a voltmeter in parallel, turn on the power pack and record the current flowing through the ammeter, and the potential difference across the voltmeter.
4. Use this data to calculate the resistance using V=IR.
5. Get a new wire which is 20cm long and connect it in place of the 10cm wire.
6. Take new measurements from the voltmeter and ammeter for each length reading.
7. Continue until the clips are 1m apart.
8. Create a table and plot a graph of the results.

Question 20

What is Ohm’s law and what are examples of ohmic conductors (conductors that obey Ohm’s law)

Answer 20

Ohm’s law states current through a conductor is directly proportional to the potential difference across it.

1. Fixed resistors
2. Wires
3. Heating elements

Question 21

How would a ohmic conductors at a constant temperature look on an IV graph?

Answer 21

It will have a straight line through the origin.

Question 22

How does a filament lamp look on an IV graph?

Answer 22

The line increases in gradient and then smooths out at the top looking like an s shape.

Question 23

Why does the line move this way?

Answer 23

As current increases, temperature increases causing an increase in resistance which slows the rate that current increases.

Question 24

How does a diode look on an IV graph?

Answer 24

Current equals 0 until the voltage threshold where current steeply increases.

This is because in the reverse direction ( negative P.D) there is reverse bias so resistance is very high resulting in near 0 current.

Question 25

What are 3 applications of thermistors?

Answer 25

Thermistors are regularly used as a thermostat, so they’re seen in: -ovens -fridges -fire alarms -digital thermometers - boilers

Question 26

What are 3 applications of LDRs?

Answer 26

- Lights that switch on in the dark - alarm clocks - burglar alarm circuits - light intensity meters - security lights

Question 27

How would we investigate resistance in thermistors and LDRs?

Answer 27

Place a thermistor/LDR in series, then place an ammeter in series and a voltmeter in parallel with the thermistor/LDR. For the LDR have a lamp with a dimming switch and for the thermistor have a heater with a dimming switch. As these change record the current and voltage to calculate the resistance.

Question 28

How would we investigate the I-V characteristics of certain components?

Answer 28

1. Create a circuit with an ammeter, voltmeter, and variable resistor, then add a fixed resistor. 2. Vary the voltage across the fixed resistor by changing the resistance in the variable resistor. Use a wide range of voltages. 3. Increase the voltage by 0.5v per reading, making sure to switch the circuit off between reading to prevent overheating. 4. Reverse the power supply to take readings for the negative current. 5. Repeat these steps with a filament lamp, and diode instead of a fixed resistor.