Topic 10 Electricity

Question 1

How do you draw a motor in an electric circuit

Answer 1

Like an ammeter but an M in the middle (MAY NOT BE NECESSARY)

Question 2

How do you draw a diode in an electric circuit

Answer 2

Like an ammeter, except the circuit wire goes through the circle and instead of an A its a triangle (similar shape to yt logo) and it has a vertical line at the right corner of the circle which isn’t too large but the middle of that line lines up with that corner of the triangle

Question 3

How do you draw an LED in an electric ciruit

Answer 3

Like a diode but with 2 small arrows pointing (from the circle) outwards

Question 4

How do you draw a thermistor

Answer 4

Like a variable resistor but you get rid of the arrow and you draw a line parallel to the resistor on the bottom of that diagonal line

Question 5

How do you draw an LDR

Answer 5

Draw a resistor, then draw a circle around it with 2 small arrows in the top right pointing inside the resistor

Question 6

Differences between series and parallel circuits

Answer 6

In series circuits, electrical components are connected one after another in a single loop. Voltage is split across components in a series circuit and current remains the same

In parallel circuits, electrical components are connected alongside one another forming extra loops. Voltage is the same across components in parallel but the current splits when there is a junction

Question 7

Recall that a voltmeter is connected __ _____ with a
component to measure the ________ _________ (______), in
volt, across it

Answer 7

in parallel
potential difference
voltage

Question 8

Explain that potential difference (voltage) is….

and hence that the volt is…

Answer 8

the energy transferred per unit charge passed

a joule per coloumb

Question 9

Recall and use the equation:

energy transferred (joule, J) =

Answer 9

charge moved (coulomb, C) × potential difference (volt, V)

E =Q×V

Question 10

Recall that an ammeter is ______ ___ ________ with a component to measure the _____, in ____ in the component

Answer 10

connected in series
current
amps

Question 11

Explain that an electric current as
and the current in metals is

Answer 11

the rate of flow of charge
a flow of electrons

Question 12

Recall and use the equation:
charge (coulomb, C) =

Answer 12

current (ampere, A) × time (second, s)

Q = I * t

Question 13

If a closed circuit includes a source of potential difference what will happen

Answer 13

In a closed circuit that includes a source of potential difference (voltage) there will be a current flowing around the circuit.

Question 14

Recall that current is conserved…

Answer 14

at a junction in a circuit

Question 15

Explain how changing the resistance in a circuit changes the
current and how this can be achieved using a variable resistor

Answer 15

Increasing the resistance in a circuit decreases the current, and decreasing the resistance increases the current.

This is because of Ohm’s Law, which states that current = voltage ÷ resistance (I = V/R).

A variable resistor can be used to change the resistance in a circuit.

By adjusting the variable resistor, you can increase or decrease the resistance, which then controls the current flowing through the circuit.

Question 16

Recall and use the equation:
potential difference (volt, V)

Answer 16

= current (ampere, A) × resistance (ohm, Ω)

V = IR

Question 17

Explain why, if two resistors are in series, the net resistance is
increased, whereas with two in parallel the net resistance is
decreased

Answer 17

In series circuits, resistance increases because adding resistors creates more obstacles for current flow, while in parallel circuits, resistance decreases because adding resistors provides more paths for current to flow.

Question 18

Total resistance in series and parallel circuits

Answer 18

Series:

R(total) = R1 + R2 + R3…

Parallel:

1/R(total) = 1/R1 + 1/R2…
Once you add up all of the resistors with a calculator, flip the fraction around to get R(total)/1

ie: 1/R(total) = 7/20 then R(total)/1 would be 20/7

Question 19

On a Voltage to current graph, what would a filament bulb, diode and fixed resistor look like

What is the behaviour of the resistance beaches of this

Answer 19

Lets say the current is on the y axis and the voltage is on the x

fixed resistor:
y = x straight graph
Resistance is constant

filament lamp:

y = x graph with hooks on the top and bottom of the graph
Resistance increases as temp increases

diode:

Exponential graph and is at 0 at all times until voltage is around 1 (only allows current to flow in 1 direction)
Resistance is very high in reverse, low in forward (after threshold)

Question 20

Construct electrical circuits to:

investigate the relationship between potential difference,
current and resistance for a resistor and a filament lamp

Answer 20

Connect a battery, variable resistor, ammeter and whatever you’re measuring (ie: resistor/bulb/diode) in series and a voltmeter around that

Question 21

Construct electrical circuits to:

b test series and parallel circuits using resistors and filament
lamps

Answer 21

1) Connect a battery, ammeter, switch and 1 resistor in series with a voltmeter around the resistor

2) Record the potential difference, Current and resistance for this resistor

3) repeat steps 1 and 2 but with 2 resistors (make sure the 2nd resistor is the same as the 1st in terms of specs) make sure the voltmeter is around BOTH resistors

4) record potential diff current and resistance for the circuit (series)

5) reorder the resistors to be parallel and the voltmeter is now around the bottom resistor and record potential diff current and resistance for the circuit

Question 22

Describe how the resistance of a light-dependent resistor
(LDR) varies with light intensity

Answer 22

The resistance of a Light-Dependent Resistor (LDR) decreases as the intensity of light incident on it increases.

In the dark and at low light levels, the resistance of an LDR is high, and little current can flow through it.

In bright light, the resistance of an LDR is low, and more current can flow through it.

Question 23

Describe how the resistance of a thermistor varies with change
of temperature (negative temperature coefficient thermistors
only)

Answer 23

A Negative Temperature Coefficient (NTC) thermistor’s resistance decreases as its temperature increases. This means that as the temperature goes up, the resistance goes down, and vice versa. This relationship is due to the semiconducting nature of the thermistor material.

Question 24

What is this question asking

Explain how the design and use of circuits can be used to
explore the variation of resistance in the following devices
a filament lamps
b diodes
c thermistors
d LDRs

Answer 24

Explain how you would set up a circuit to do this

ie: ammeter here, battery here, voltage inc by 2 from 2 to 12 etc

Question 25

Recall that, when there is an electric current in a resistor, and what can it be described as

Answer 25

there is an energy transfer which heats the resistor. The energy transfer can be described as the result of collisions between electrons and the ions in the lattice

Question 26

Explain that electrical energy is dissipated as thermal energy in the surroundings when

Answer 26

an electrical current does work against electrical resistance

Question 27

Explain ways of reducing unwanted energy transfer through low resistance wires

Answer 27

power = current2 × resistance The equation shows that a high current will have a much higher heating effect on the transmission wires than a low current. For this reason, transmitting energy at a high voltage with a low current will keep the wires cooler and waste less energy. Reducing the resistance of the wires will also reduce unwanted energy transfer, but reducing the current will have a much more significant effect.

Question 28

Describe the advantages and disadvantages of the heating effect of an electric current

Answer 28

The heating effect is very useful in appliances which are intended to heat up, such as: Electric kettles Electric ovens Electric toasters It results in energy loss, reducing efficiency For example, waste heat in a light bulb or overheating in a computer It can pose a fire hazard – many domestic fires are caused by too much current passing through low-quality wiring For example, sparks or excessive heat in an electric motor

Question 29

Use the equation: energy transferred (joule, J) =

Answer 29

current (ampere, A) × potential difference (volt, V) × time (second, s) E = I * V * t

Question 30

Describe power as... and recall that it is measured in ____

Answer 30

the energy transferred per second watt

Question 31

Recall and use the equation: power (watt, W) =

Answer 31

energy transferred (joule, J) ÷ time taken (second, s) P = E/t

Question 32

Explain how the power transfer in any circuit device is related to the potential difference across it and the current in it

Answer 32

Potential Difference (Voltage): Voltage represents the electrical potential energy available to move charge (electrons) through the circuit. It's the "push" that causes the current to flow. Current: Current is the rate of flow of electrical charge (electrons) through a conductor. It's measured in amperes (A). Power: Power is the rate at which energy is transferred or consumed by the device. It's the product of voltage and current, as stated in the equation P = V * I so they are directly related

Question 33

Recall and use the equations: electrical power (watt, W) = electrical power (watt, W) =

Answer 33

current (ampere, A) × potential difference (volt, V) P = IV current squared (ampere2, A2) × resistance (ohm, Ω) P = I^2 R

Question 34

Describe how, in different domestic devices, energy is transferred from batteries and the a.c. mains to the energy of motors and heating devices

Answer 34

Heating devices such as kettles transfer energy electrically from the mains a.c supply to the thermal energy store of the heating element inside the kettle. Energy is transferred electrically from the battery of a handheld fan to the kinetic energy store of the fan's motor.

Question 35

Describe direct current (d.c.) as... and recall that ___ and ______ supply direct current (d.c.)

Answer 35

movement of charge in one direction only cells and batteries

Question 36

Describe that in alternating current (a.c.) the movement of charge _____ ________

Answer 36

changes direction

Question 37

Recall that in the UK the domestic supply is ____, at a frequency of __ Hz and a voltage of about ___ V

Answer 37

a.c 50 230

Question 38

Explain the difference in function between the live and the neutral mains input wires

Answer 38

The live wire carries the electrical current from the power supply to the appliance, having a potential difference of around + or -230V. The neutral wire completes the circuit by providing a return path for the current back to the power source, typically at 0V. If the live wire is negative it is relatively negative to the neutral and same for positive

Question 39

Explain the function of an earth wire and of fuses or circuit breakers in ensuring safety

Answer 39

The earth wire provides a safe, low-resistance path for current to flow if a fault occurs, preventing electric shocks. Fuses and circuit breakers act as overcurrent protection devices, interrupting the circuit if too much current flows, preventing damage and fire.

Question 40

Explain why switches and fuses should be connected in the live wire of a domestic circuit

Answer 40

Safety when switched off: If a switch were in the neutral wire, the appliance would still be connected to the live wire even when switched off, posing a risk of electric shock if the user touched the appliance. Fault protection: If a fault occurs, such as a faulty component touching the metal casing of the appliance, the live wire and the earth wire will provide a low-resistance path for the current to flow. The high current will cause the fuse to melt, breaking the circuit and preventing a shock.

Question 41

What is the potential difference of the earth wire

Answer 41

0V This wire is for safety and provides a low-resistance path for current to flow to the ground in case of a fault. It's usually green and yellow in a UK plug and is at 0 V.

Question 42

Explain the dangers of providing any connection between the live wire and earth

Answer 42

Connecting the live wire to the earth wire is extremely dangerous because it creates a low-resistance path for a large current to flow, potentially leading to a severe electric shock or even electrocution. This occurs because the live wire carries a significant potential difference (+-230V) relative to the earth (0V), and any connection between them will cause a large current to flow.

Question 43

Describe, with examples, the relationship between the power ratings for domestic electrical appliances and the changes in stored energy when they are in use

Answer 43

Explanation: Power is the rate of energy transfer: Power, measured in Watts (W), indicates how much energy an appliance uses per second. Higher power, faster transfer: An appliance with a higher power rating, like a 2000W kettle, transfers more energy per second than a lower-powered appliance, like a 50W lamp. Energy transfer and use: Appliances transfer electrical energy to other forms, like heat, light, or motion, to perform their function. The power rating reflects the rate at which this transfer occurs. A 2000W electric kettle will heat water faster than a 1000W kettle. A 1500W hair dryer will heat the air faster than a 500W hair dryer. A 1000W electric fan will produce more airflow than a 500W fan.