Electrical Physics

Question 1

Charge

Answer 1

Fundamental property of some matter. Like charges repel, opposite charges attract

Question 2

Neutral

Answer 2

Object with equal amounts of positive and negative charge. Low energy, stable state.

Question 3

Separation of Charge

Answer 3

If negative charges are separated from positive charges, both gain electrostatic potential energy, unstable state.

Question 4

Potential Difference (voltage)

Answer 4

Change in potential energy for charged particles between two points.

Question 5

Static Electricity

Answer 5

Stationary build-up of positive or negative charge. Stores large amount of electrostatic potential energy, unstable state.

Question 6

Potential drop

Answer 6

Decrease in potential energy for charged particles between two points.

Question 7

Volts

Answer 7

Units for voltage, potential difference, electromotive force, potential drop. 1 V = 1 J C-1

Question 8

Current Electricity

Answer 8

Flow of charged particles from high electrostatic potential energy to low electrostatic potential energy. E.g. electrons flowing towards lone protons.

Question 9

Current

Answer 9

Rate of flow of charge.

Question 10

Amperes (amps) A

Answer 10

Units for current. 1 A = 1 C s-1

Question 11

Resistance

Answer 11

Measure of how difficult it is for current to pass through a substance.

Question 12

Decreasing Resistance

Answer 12

Lower temperature, increase diameter of wire, decrease length of wire, change material e.g. Au<Cu<Fe.

Question 13

Ohms

Answer 13

Units for resistance. 1 Ω = 1 V A-1

Question 14

Power

Answer 14

The rate that a circuit component transfers or transforms energy.

Question 15

Watts

Answer 15

Units for power. 1 W = 1 J s-1

Question 16

Series circuits

Answer 16

Circuits (or parts of a circuit) with only 1 path for current to flow through.

Question 17

Voltage in series

Answer 17

Each component in series add to/takes from the total voltage for the circuit

Question 18

Current in series

Answer 18

Constant

Question 19

Resistance in series

Answer 19

Each component in series adds to the total resistance for the circuit.

Question 20

Parallel Circuits

Answer 20

Circuits (or parts of a circuit) with 2 or more paths for current to flow through.

Question 21

Voltage in parallel

Answer 21

Each parallel path receives the total voltage for the circuit.

Question 22

Current in parallel

Answer 22

Each parallel path allows more current to flow, adding to the total current for the circuit.

Question 23

Resistance in parallel

Answer 23

Each parallel path decreases the total resistance for the circuit.

Question 24

Advantages of parallel over series

Answer 24

Each device can be turned on/off independently, if one breaks the others continue functioning. Each device receives the full voltage from the power supply.

Question 25

Disadvantage of parallel

Answer 25

Each additional parallel path increases total current, can eventually lead to dangerous levels of current.

Question 26

Dangers of current electricity

Answer 26

Large current cause heating in wires which can start fires. Exposure to high voltage wires can allow current to flow through humans to the ground causing burns, stopping the heart and creating toxins in the body.

Question 27

Mains power in Australia

Answer 27

Alternating current in Australia changes direction with a frequency of 50 Hz. 240V

Question 28

Electron flow

Answer 28

The direction that negatively charged particles move in a circuit (negative to positive).

Question 29

Conventional current

Answer 29

The direction that positively charged particles move in a circuit (positive to negative).

Question 30

Short circuit

Answer 30

If the load in a circuit is bypassed the resistance will be too low, leading to dangerously high currents.

Question 31

Fuse

Answer 31

Function as normal part of active wire during normal operation. If current becomes too high (e.g. short circuit) it rapidly breaks, cutting the circuit, preventing a fire.

Question 32

Circuit breaker

Answer 32

If current in active wire becomes too high (e.g. short circuit) it rapidly turns off the circuit using an electromagnet, preventing a fire.

Question 33

Residual current device

Answer 33

Compares current in active and neutral wires, if there is a difference (e.g. accidental grounding) it rapidly turns off the circuit using an electromagnet, preventing electrocution.

Question 34

Double insulation

Answer 34

Device where there is no way for active wire to come in contact with case of device, no need for Earth wire.

Question 35

Active Wire

Answer 35

Supplies 240 V, 50 Hz AC voltage, part of the circuit.

Question 36

Neutral Wire

Answer 36

Completes circuit, grounded. Zero potential to earth.

Question 37

Earth wire

Answer 37

Not part of the circuit, connects metal case of device to ground to prevent electrocution.

Question 38

Elementary charge

Answer 38

The elementary charge, e, of a proton is equal to +1.6 × 10−19 C.
The elementary charge, −e, of an electron is equal to −1.6 × 10−19 C.

Question 39

Negatively charged particles

Answer 39

An excess of electrons causes an object to be negatively charged, and a deficit in electrons will mean the object is positively charged.

Question 40

Net charge

Answer 40

When electrons move from one object to another, each object is said to have gained a net charge. The object that loses the electrons will have a net positive charge, since it will now have less negative electrons than positive protons.When an atom has gained or lost electrons, you say it has been ionised or has become an ion.

Question 41

Variables that affect resistance: Wire length

Answer 41

A longer piece of wire, the electrons bump into more ions along the way, so more energy would be needed for the electrons to travel from one end to the other. In other words, a longer piece of wire would provide greater ‘resistance’ to the flow of electric current.

Question 42

Variables that affect resistance: Wire Thickness

Answer 42

A thicker piece of wire allows more electrons to flow through it at the same time, much like a dual- lane highway allows faster traffic flow than a single lane. In practice, the cross-sectional area of the wire (its area when viewed end on) is important. The greater the cross-sectional area of the wire, the lower its resistance will be.

Question 43

Temperature and Resistance

Answer 43

Increasing the temperature of a piece of copper wire means that the copper ions will vibrate back and forth more quickly. This makes it more likely that an electron will collide with the ion as it moves past it. Therefore, increasing the temperature of the wire also increases the resistance of the wire.

Question 44

Ohms Law

Answer 44

current flowing through it was directly proportional to the potential difference across it:

Question 45

Kirchhoffs Loop Rule

Answer 45

The energy given to the charges (potential gain) must be equal to the energy lost by the charges (potential drop). In a series circuit, the energy loss will be spread across the different components.

Question 46

AC

Answer 46

This means that the electrons in the wire oscillate backwards and forwards in the wire

Question 47

DC

Answer 47

In comparison, a battery provides direct current (DC), which means the electrons travel in one direction only.

Question 48

Fuse or Circuit breaker

Answer 48

The function of both of these components is to interrupt the flow of current if it exceeds a certain value. Unlike a fuse, a circuit breaker can be easily reset after it has been activated, whereas a fuse needs to be physically replaced once it has melted through.

Question 49

Earth wires

Answer 49

If the active wire inside the appliance becomes loose and touches the case, then the whole case becomes electrically live. If anyone touches the case, the current will flow through their body, with possibly fatal consequences. To prevent this, an earth wire is permanently connected to the metal case of the appliance. If the active wire touches the case, a short circuit will be created and current will immediately flow directly to earth. The large amount of current that flows in this situation should trip the fuse or circuit breaker, alerting users of the appliance to the problem.

Question 50

Double Insulation

Answer 50

Two insulating barriers to protect users. Often this is done by making the case of the appliance out of plastic. This acts as an insulating layer in addition to the plastic insulation surrounding the active wire inside the appliance. Double-insulated appliances do not need an earth wire, so their electrical plugs only have two pins.

Question 51

RCD Residual Current Devices

Answer 51

Detect any difference between the current in the active wire and the current in the neutral wire. In a properly operating circuit, these two currents should be exactly the same, but in opposite directions.The most likely reason for a difference between the active and neutral currents is that some current is going to earth through a fault or, in a worse case, through a person. If this happens, the RCD is able to switch off the supply in about 20 milliseconds, hopefully preventing any serious harm.

Question 52

Electrical Shock

Answer 52

The effect of electric shock depends on a number of factors including:
the amount of current passing through the body
its duration
the path it takes through the body.