Electricity & Circuits

Question 1

Series vs parallel

Answer 1

S - one loop, current is the same everywhere, voltage splits (shared, so bulbs are dimmer), total resistance increases (only one path for electrons to flow)
P - more than one loop, current splits at a junction then rejoins, voltage stays the same (bulbs are bright and stay that way), total resistance decreases (other paths for the electrons to take)

Question 2

Voltmeter

Answer 2

Connected in parallel. Measures potential difference in volts

Question 3

Voltage

Answer 3

The energy transferred per unit charge. Measured in volts (joule per coulomb) by a voltmeter. Measure the difference in potential energy between two points in a circuit

Question 4

Energy transferred (equation)

Answer 4

(Joule) = charge moved (coulomb) x potential difference (volt)
E=QV

Question 5

Ammeter

Answer 5

Connected in series, measures the current in amps

Question 6

Electric Current

Answer 6

Rate of flow of charge

Question 7

Current in metals

Answer 7

Flow of electrons

Question 8

Charge (equation)

Answer 8

(coulomb) = current (amps) x time (secs)

Q=It

Question 9

Junction

Answer 9

Where the electrons can goes more than one way

Question 10

Current at junctions

Answer 10

Conserved. Total current before the split is the same after

Question 11

Mains power supply UK

Answer 11

230V at 50Hz frequency

Question 12

Resistance

Answer 12

The opposition of current / how difficult it is for electricity to flow. Measure is ohms

Question 13

Potential difference (equation)

Answer 13

(Volt)= current (amps) x resistance (ohms)

V=IR

Question 14

Effect of changing the resistance

Answer 14

Changes the current. By using a variable resistor (increase resistance, current decreases to obtain the same overall voltage)

Question 15

Variable resistor

Answer 15

Changes the resistance and therefore the current (in the power pack). Can adjust resistance value.

Question 16

Series circuit design and construction for testing and measuring

Answer 16

Voltmeter - voltage in parallel
Current - ammeter in series
Cell or battery, wires, device to measure (filament bulb, diode, resistor)

Question 17

Fixed resistors

Answer 17

Offer a set resistance

Question 18

Current compared to resistance

Answer 18

Current decreases
Inversely proportional
I alpha 1/R

Question 19

Potential difference compared to resistance

Answer 19

Potential difference Increases

Question 20

Ohms law

Answer 20

I alpha V (if resistance stayed the same and potential difference increased
V=IR

Question 21

Heating effect

Answer 21

When electrons collide with atoms or ions in the lattice. Energy is transferred and atoms vibrate more. This causes heat.

Question 22

Advantages of heating effect

Answer 22

Electrical heaters, heat bulbs, toaster

Question 23

Disadvantages of heating effect

Answer 23

Overheating, computers, burns

Question 24

Filament lamp

Answer 24

S shape. Can only take so much current due to more current resulting in higher temperatures
The resistance of a lamp increases as the temperature increases due to electrons colliding with ions in the metal, making current harder to flow and causing resistance

Question 25

Diode

Answer 25

J shape. Only let current go one way. The resistance is infinite since nothing is happening in the negative direction. The current gets really high above 0.6V. This shows that the resistance in the positive direction is really low. Used to convert alternating current to direct current. When forward-biased, the resistance is large at low potential differences but at high potential differences, resistance quickly drops and a current begins to flow

Question 26

Fixed resistors

Answer 26

Offer a set resistance that cannot change. Diagonal line. The current and potential difference are directly proportional to each other. As current decreases, potential difference increases in proportion. This means that the resistor follows Ohms law. However, this only happens if the temperature stays the same

Question 27

Greater temperature means

Answer 27

Greater resistance due to more collisions

Question 28

Thermistor

Answer 28

Resistance varies with change of temperature. High temp gives low resistance and vice versa. They can be used for automatic heaters, thermostats and heat activated fire alarms

Question 29

LDR

Answer 29

Light dependant resistors are affected by light intensity. If light intensity is high, resistance is low and vice versa. They can be used for automatic street lamps and sensors in cameras

Question 30

When there is an electrical current in a resistor

Answer 30

There is an energy transfer which heats the resistor due to collisions between electrons and ions in the lattice

Question 31

What happens when an electrical current works against electrical resistance?

Answer 31

Electrical energy is dissipated as thermal energy in the surroundings (electrons colliding with ions and transferring their energy)

Question 32

Ways of reducing unwanted energy transfer

Answer 32

Through low resistance wires and diodes

Question 33

Energy transferred (don't need to memorise equation)

Answer 33

``` (Joule) = current x potential difference x time E = IVt ```

Question 34

Power definition

Answer 34

(Rate of work done) the energy transferred per second, measured in watt

Question 35

Power (equation)

Answer 35

``` Energy transferred / time taken P=E/t Current x potential difference P=IV Current squared x resistance P=I^2 x R ```

Question 36

Energy transferred from batteries and the ac mains

Answer 36

To the energy of motors and heating devices

Question 37

Direct and alternating voltage difference

Answer 37

...

Question 38

Direct current

Answer 38

Movement of charge in one direction only. Cells and batteries

Question 39

Alternating current

Answer 39

Movement of charge that changes direction. Mains power supply

Question 40

Live wires

Answer 40

230V. Brown wire. Right side. Provides the current

Question 41

Neutral wire

Answer 41

0V. Blue wire. Left side. Completes the circuit

Question 42

Earth wire

Answer 42

0V. Green and yellow. Top. | Provide an alternative path for current if appliances develop faults

Question 43

What happens if the live wire becomes loose and touches the metal case?

Answer 43

A very large current flows to earth and blows the fuse, breaking the circuit

Question 44

What are the wires connected to?

Answer 44

Terminals

Question 45

Fuse

Answer 45

A built in weak point in a circuit. Contain a thin wire with a higher resistance than normal wire. When a large current flows, the wire becomes hot. If it is too hot the overcoat melts and breaks the circuit 3, 5 or 13A (higher than the operating current)

Question 46

Circuit breakers

Answer 46

Like fuses but are electromagnetic switches which are easy to reset. Too much current makes the magnetic field strong enough to open the switch which "trips" the circuit

Question 47

Why should switches and fuses be attached to the live wire

Answer 47

It carries the current

Question 48

Dangers of connecting the live wire and earth

Answer 48

Electrocution

Question 49

Potential difference def

Answer 49

A measure of how much energy is transferred between two points in a circuit

Question 50

Investigating current and resistance relationship

Answer 50

With a filament bulb, fixed resistor and diode. Use a variable resistor (i.e. power pack) and make sure voltage is low to start. Record current reading on ammeter (after component in circuit). Increase voltage and record current. Repeat and increase voltage by 0.5-1 V. Repeat but reverse the power supply (negative direction).

Question 51

Ohmic conductor

Answer 51

Fixed resistors obey Ohm's Law where potential difference and current are proportional