Topic 10: Electricity and Circuits

Question 1

10.1 Describe the structure of the atom, limited to the position, mass and charge of protons, neutrons and electrons

Answer 1

central nucleus containing protons + neutrons (therefore a positive charge and contain the mass)

has electrons found at different distances from the nucleus in shells

electrons are negative, charge is equal but opposite to protons and have the same quantities

atoms uncharged

Question 2

10.2 Draw and use electric circuit diagrams representing them with the conventions of positive and negative terminals, and the symbols that represent cells, including batteries, switches, voltmeters, ammeters, resistors, variable resistors, lamps, motors, diodes, thermistors, LDRs and LEDs

Answer 2

positive and negative terminals- conventional current direction goes from the positive to the negative terminal of a battery

cells-long line (pos) next to thick line (neg)

batteries- line, shorter thick line, dotted line to long line (pos), shorter thick line

switches- open= small circle attached to line going up, unattached to another small circle

voltmeters-circle + V

ammeters-circle + A

resistors-rectangle (not filled in)

variable resistors-rectangle (arrow going across and up through it)

lamps- circle with cross

motors-circle + M

diodes-circle with a line through, line then triangle >(without line through)

thermistors-rectangle with line under going sideways, then line going up through cell

LDRs-rectangle, two arrows pointing down

LEDs- line, triangle pointing >, line at base + two arrows pointing up at base

Question 3

10.3 Describe the differences between series and parallel circuits

Answer 3

series - one route the current can take around the circuit. lamps cannot be switched on and off individually and if one lamp fails they will all switch off

parallel - junctions that allow the current to take different routes. each lamp can be switched separately and if one light stops working, they will still all work

Question 4

10.4 Recall info about a voltmeter

Answer 4

is connected in parallel with a component to measure the potential difference (voltage), in volt, across it

Question 5

10.5 Explain info about potential difference (voltage)

Answer 5

PD is the energy transferred per unit charge passed and hence that the volt is a joule per coulomb

needed to ‘push’ current around an electrical circuit

bigger PD, bigger current

PD across each branch of the circuit is the same

Question 6

10.6 energy transfer equation

Answer 6

energy transferred (joule, J) = charge moved (coulomb, C) × potential difference (volt, V)

QEV (quenton eats veg)

Question 7

10.7 Recall info about an ammeter

Answer 7

ammeter is connected in series with a component to measure the current, in amp, in the component

Question 8

10.8 Explain info about an electric current

Answer 8

moving charged particles form an electrical current. is the rate of flow of charge and the current in metals is a flow of electrons

measured in amperes (amps) using an ammeter

Question 9

10.9 charge equation

Answer 9

charge (coulomb, C) = current (ampere, A) × time (second, s)

Question 10

10.10 Describe how current occur

Answer 10

for current to flow, circuit must be closed and contain a source of PD (eg cell or battery)

Question 11

10.11 describe currents at a junction in a circuit

Answer 11

conserved

Question 12

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

Answer 12

as I = V /R , this reduces the current flowing through the circuit and changes the p.d across the component.
each time you use a variable resistor to alter the current, record the p.d difference across the component and the current through it and repeat each reading twice calculating an average p.dd for each current.
you can also reverse the wires connected to the battery to reverse the direction of current.

Question 13

10.13 Recall the potential difference equation

Answer 13

V = I x R
potential difference (v) = current (a) x resistance (ohms)

Question 14

10.14 Explain what happens if two resistors are in a series

Answer 14

it means that two resistors have to share the total p.d so the p.d across each resistor is lower so the current through each resistor is lower.

Question 15

10.15 Calculate the currents, potential differences and resistances in series circuits

Answer 15

potential difference in series circuits : Vtotal = V1 + V2 (+… etc)
total circuit p.d = p.d across component 1 + p.d across component 2
current in series circuits: Itotal =I1 =I2 = …etc
total current flowing in circuit = current through component 1 = current through component 2 = … etc
resistance in series circuit = Rtotal + R1 + R2 + …etc
total resistance in circuit = resistance of component 1 + resistance of component 2 + …etc

Question 16

10.16 Explain the design and construction of series circuits for testing and measuring

Answer 16

in a series circuit the different components are connected in a line, end to end, between the positive and negative ends of the power supply (apart from voltmeters as they are always connected across a component.
series circuits are often designed to build and measure components because the p.d, current and resistance are quite easy to change, measure and calculate.

Question 17

10.17 Recall the core practical : Constructing electric circuits

Answer 17

a) set up circuit. use a power pack that provides different p.ds. set power pack to its lowest voltage and switch on. write down readings on ammeter and voltmeter and then switch of power pack. repeat for five different voltage settings up to max of 6V. replace the resistor in the circuit with two filament lamps and repeat.
b) construct circuit using one resistor. measure the current through the circuit using the ammeter. use this and the p.d of the battery to calculate the resistance of the circuit using R = V / I. add another resistor in series with the first. again, measure the current through the circuit sonf use the p.d of the battery to calculate overall resistance of the circuit. repeat these strips until you’ve added all resistors.

Question 18

10.18 Explain how current varies with potential difference for certain devices and how it relates to resistance

Answer 18

filament lamp - as more current flows through the lap, resistance increases so less current p.d per unit
diodes - only lets current pass through it in one direction so depends
fixed resistors - directly proportionate to p.d.

Question 19

10.19 Describe how resistance of a LDR varies with light intensity

Answer 19

a light dependant resistor is dependant on the intensity of light
in bright light the resistance falls
in darkness the resistance is highest.
use a torch to shine light on LDR and record the distance between the torch and LDR gradually moving it away so the intensity decreases. record the intensity every 10cm you move away and then calculate resistance of LDR for different light intensities. you should find that the LDR’s resistance increases each time.

Question 20

10.20 Describe how the resistance of a thermistor varies with changes of temperature

Answer 20

a thermistor’s resistance decreases as the temperature increases + varies with change of temp.
in hot conditions, the resistance drops.
in cool conditions, the resistance goes up
a good way of controlling it is through a water bath - measure and record temp of eater and measure the current through the circuit for every 5 degrees and us p.d to find the resistance at each temperature

Question 21

10.21 Explain how the design and use of circuits can be used to explore the variation of resistance in certain devices

Answer 21

filament lamp - when an electrical charge flows through it, it transfers some energy to thermal energy store to heat up and glow. resistance increases with temperature so as more current flows through the lamp , resistance increases meaning less current can flow per unit p.d.
diodes - only lets current pass through it in one direction so the resistance depends on the direction
thermistors - as current flows through it, it hears up causing resistance to decrease.
LDRs - if light level is kept constant during the experiment, it will behave like a fixed resistor.

Question 22

10.22 Recall what happens when there is an electric current in a resistor

Answer 22

when there is an electric current in a resistor, there is an energy transfer which heats the resistor.

Question 23

10.23 Explain what happens to electrical energy when it is dissipated

Answer 23

electrical energy is dissipated as thermal energy in the surroundings when an electrical current does work against the electrical resistance.

Question 24

10.24 Explain the result of energy transfer

Answer 24

free electrons collide with the ions that make up the lattice and these collision transfer energy from the electrons to the ions, making the ions vibrate and causing the resistor to heat up

Question 25

10.25 Explain ways of reducing unwanted energy transfer through low resistance wires

Answer 25

one way is through using low resistance wires - without it less energy is being transferred to useful energy stores and can cause components in a circuit to melt.

Question 26

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

Answer 26

advantage - fuses help protect circuits as they melt and break a circuit if the current gets too high - preventing fires
disadvantage - can reduce efficiency as less energy is being transferred to useful stores and circuit can melt which can stop it from working properly.

Question 27

10.27 energy tranfer equation

Answer 27

energy transferred (j) == current (a) x potential difference (v) x time (s)

Question 28

10.28 Describe power and recall how it is measured

Answer 28

the power of an appliance is the energy that it transfers per second so power tells us how quickly energy is transferred.
appliances can be given a power rating which is labelled with the max power that it can operate at

Question 29

10.29 Recall the power equation

Answer 29

P = E/T
power (w) = energy transferred (j) / time taken (s)

Question 30

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

Answer 30

the power of an appliance also depends on the p.d across it and the current through it so the higher the p.d, the more powerful the appliance.

Question 31

10.31 Recall and use the electrical power equations

Answer 31

P = I x V
electrical power (w) = current (a) x potential difference (v)
if you don’t know the p.d then u can use:
P = I* x R
electrical power (w) = current squared (a) x resistance (ohms)

Question 32

10.32 Describe how in different domestic devices, energy is transferred

Answer 32

the power rating of an appliance is measured in watts. a kettle with a power rating of 3kw transfers 3000 joules of energy each second ( from the mains energy supply to a store of thermal energy in the water).

Question 33

10.33 Explain the difference between direct and alternating voltage

Answer 33

alternating voltage is where the positive and negative ends of the p.d keep switching whereas for direct voltage the positive and negative ends are fixed

Question 34

10.34 Describe direct current

Answer 34

direct current is a current in which the charges only move in one direction. cells and batteries supply direct current.

Question 35

10. 35 Describe the movement of charge changes direction in alternating current

Answer 35

the frequent (how of often the current changes direction) is 50 cycles per second or 50 Hz.

Question 36

10.36 Recall what the UK domestic supply is

Answer 36

supply is the UK domestic supply is an a.c at around 230V and frequency of 50Hz.

Question 37

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

Answer 37

live wire - brown. what provides the electricity from the mains supply - blue - completes the circuit an carries away current. is around 0v
earth wire - green and yellow is also at 0v used for protecting wiring and for safety.

Question 38

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

Answer 38

earth wire - stops the appliance casing from becoming live.
fuses - the thicker the cable the higher the fuse rating (the higher the current, the wire could get too hot and the fuse blows and the circuit is broken.
circuit breakers - they turn off quicker than the time taken for a fuse to melt if there’s a current flow and can also be reset which is much easier than having to replace a fuse.

Question 39

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

Answer 39

because they are used to break circuits so if there is a problem, the supply to the electricity to the appliance can be cute off.

Question 40

10.40 Recall the potential difference between the live, neutral and earth mains wires

Answer 40

the p.d between the live and neutral wire is230V and the p.d between the live and earth is also 230V, and there is no p.d between neutral and earth.

Question 41

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

Answer 41

if the link creates a low resistance path to the earth wire, a huge current will flow, which could result in a fire.

Question 42

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

Answer 42

the power rating tells you the maximum amount of energy transferred between stores per second when the appliance is in use which helps customers choose between models - the lower the power rating, the less electricity used in the appliance so the cheaper it is to run.