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Science Year 2 > Electrical systems > Flashcards

Electrical systems Flashcards

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1
Q

What are the three effects of electricity?

A

Chemical effects (Electrolysis)
Magnetic effects (Electromagnetism)
Heating and Lighting effects

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2
Q

Describe the application of chemical effects such as electrolysis .

A

Electroplating— coated with metal to prevent rusting so they would coat it with unreactive metals such as copper,silver and gold

Extraction of metals (e.g. aluminium from bauxite ore)

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3
Q

Describe the application of magnetic effects (electromagnetism)

A

Scrapyards and motors of electric fans/DVD drives

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4
Q

Describe the application of heating and lighting effects.

A

Heating elements of electric kettles
Heating and lighting of light bulb filaments.

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5
Q

When is an electric current formed?

A

An electric current is formed when charges move.

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6
Q

In order for ionic compounds to conduct electricity, there must be ________. What should the blank be?

A

Free-moving charge carriers

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7
Q

What is the conventional current flow?

A

Positive charges flow from the positive terminal of the battery to the negative terminal of the battery.

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8
Q

What is electron flow?

A

Electron flow is denoted to be the movement of electrons from a negatively charged end towards a positively charged end.

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9
Q

What is the definition of current?

A

Current is defined as the rate of flow of electric charge.

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10
Q

What is an ammeter used for and it should be connected in____ to the circuit?

A

Ammeter is used to measure current in a circuit. It must be connected in series to the circuit.

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11
Q

Should an ammeter have infinite resistance or no resistance and why?

A

An ammeter should have zero resistance to the current flow, such that the presence of the ammeter does not affect the quantity that it is measuring. (Based on notes)

Based on WS ans—> An ammeter should have a very low resistance to ensure that a large current flows through the ammeter and the current that flows through the ammeter is as close as possible to the original current like as if there is no ammeter so that one can get an ACCURATE READING.

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12
Q

What are the two different types of voltages?

A

Potential difference and electromotive force

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13
Q

What is the definition of potential difference?

A

potential difference (p.d.) across a component in an electric circuit is the work done to drive a unit charge through the component.

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14
Q

What is the definition of electromotive force?

A

The electromotive force (e.m.f.), of an electrical source is the work done by the source to drive a unit charge around a complete circuit.

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15
Q

Both p.d. and e.m.f. Have the same S.I. Unit—— ______?

A

Volt (V)

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16
Q

What is a voltmeter used for and it must be connected in ____ with the component?

A

Voltmeter is used to measure the potential difference across two points in a circuit. The voltmeter must be connected in parallel with the component.

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17
Q

Should a voltmeter have infinite resistance or no resistance and why?

A

A voltmeter should have infinite resistance so that no current passes through it. Otherwise, the voltmeter would affect the quantity that it is measuring. (Based on OneNote)

(based on WS ans)
Voltmeters should have a very high resistance to ensure that very little current flow through voltmeter and current only passes through the circuit components that the voltage is in parallel with. This also PREVENTS A SHORT CIRCUIT of the circuit component (e.g. light bulb)

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18
Q

What is a trick to solve electric current readings if there are no numbers?

A

Add in NUMBERS!!!

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19
Q

What is another way to represent volts other than the formula V=RI?

A

Volts=Joules/Columb

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20
Q

What is another way to represent ampere other than the formula V=RI?

A

Ampere=Columb/Second

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21
Q

If a monkey stands on a single wire with a very high voltage and then jumps onto another wire with a lower voltage, and at this moment the monkey’s legs are on the wire with a high voltage and its hands is on the wire with a low voltage, what would happened to the monkey and why?

A

There would be sparks of fire seen and the monkey would possibly die. This is because electrons flow from a higher electrical potential energy to a lower electrical potential energy and therefore current will flows the monkey’s body and some of the electric energy would be converted to heat energy which is why sparks of fire can be seen.

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22
Q

When does an open circuit occurs?

A

An open circuit occurs when there is a break in the circuit to stop the current from flowing.

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23
Q

What are the four main components that an electrical circuit consists of?

A
  1. An electrical source that drives the electric charge around the circuit (e.g. battery)
  2. A load on which moving charges can do a useful job (e.g. a lamp or resistor)
  3. Conductors to connect the components together (e.g. copper wire)
  4. Switches to open or close the circuit
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24
Q

Draw the symbol of these devices in notability.
Switch, cell, battery, wires joined, wires crossed, lamp, fixed resistor, variable resistor (or rheostat), fuse, ammeter, voltmeter.

A

Answers are found in OneNote

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25
Q

Explain resistance.

A

Resistance can be understood as the HINDRANCE to the FLOW of charge which causes ELECTRICAL ENEGY to be LOST and CONVERTED to OTHER FORMS OF ENERGY.
For e.g. (light energy in a light bulb , heat energy in a kettle, or mechanical energy in a fan).
The resistance of a conductor is a measure of the OPPOSITION an electric current experiences when it flow through it.
The resistance of a component is defined as the RATIO of the potential difference across it to the current flowing through it.

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26
Q

What is the S.I. unit for resistance?

A

Ohm (semicircle) i think you understand what is the sign

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27
Q

All components in a circuit (including its source) have some resistance. True or false?

A

True
However, in an ideal situation, the source and the wires have ZERO resistance

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28
Q

A resistor is a conductor in a circuit that has a known value of resistance and is mainly used to _______.

A

Control the size of current flowing in a circuit.

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29
Q

What are the two types of resistors?

A

Fixed and variable resistors.

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30
Q

What is a fixed resistors?

A
  1. Fixed resistors have fixed value of resistance.
  2. Examples include carbon film resistors, carbon composition resistors, tin oxide resistors and wire-wound resistors.
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31
Q

What is an example of variable resistors?

A

A rheostat is an example of variable resistor.

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32
Q

What is a variable resistor? Describe how it works.

A

Variable resistors are resistors with changing resistances. As the slider is moved to the right, the current has to pass through a longer length of constantan wire which translates to higher resistance of the variable resistor.

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33
Q

What is effective resistance?

A

When there are two or more resistors in a circuit, the combined effect of their presence can be calculated. This is known as the effective resistance of the resistors.

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34
Q

How do you calculate the effective resistance of R1 and R2 and R3 connected in series?

A

Reff= R1 +R2 +R3

35
Q

Is current split or same in series?

A

Same

36
Q

Is voltage same or split in series?

A

Split

37
Q

Is current split or same in parallel?

A

Split

38
Q

Is voltage split or the same in parallel?

A

Same

39
Q

How do you calculate the voltage in series?

A

V total=V1+V2+V3

40
Q

How do you calculate the total resistance of the resistors in parallel?

A

1/R eff= 1/R1 + 1/R2 +1/R3

41
Q

How do you calculate the sum of current passing through the individual resistors connected in parallel.

A

I total= I1 + I2 +I3

42
Q

What is the definition of power.

A

Power is defined as the amount of electrical energy converted to other forms of energy per unit time by the component.

43
Q

What is the formula of power?

A

Power=Potential difference X Current P=VI

44
Q

What is the S.I. Unit of power?

A

Watt (W) recall that w=j/s

45
Q

What is the symbol of current?

A

Symbol: I

46
Q

What is the SI unit of current?

A

Ampere (A)

47
Q

What is the symbol of voltage

A

V

48
Q

What is the symbol of resistance?

A

R

49
Q

What is the symbol of physical quantity of power?

A

P

50
Q

What is the symbol of energy?

A

E

51
Q

What is the SI unit of energy?

A

Joule (J)

52
Q

How do you calculate the amount of electrical energy used by the appliance?

A

Energy=Power X Time
E=Pt=VIt

53
Q

What are the three formula of power which is essentially the same just that the way you express it is different?

A

P=VI=I square R=V square divide by R

54
Q

What is the ratio method for current in parallel?

A

Since R1:R2 (in //)
2: 3
Then. I1: I2
1/2: 1/3
3:2 (common denominator is 6)
I1= 3/(3+2) X IT
= 3/5 X5
=3.00A
I2= 2/(3+2) X IT
= 2/5 X 5
=2.00A

54
Q

1kw= ? W

A

1000W

54
Q

The ratio method in // is used to find what?

A

Current

55
Q

The ratio method in series is used to find what?

A

Voltage

56
Q

What is the ratio method for voltage/pd in series?

A

Since R1:R2 in series
1: 1.2
Then. V1:V2
1:1.2
V1= 1/(1+1.2) X VT
=5.00V
V2=1.2/(1+1.2) X VT
=6.00V

57
Q

What are the three situations involving the dangerous use of electricity?

A

Frayed electric cord, electrical appliance used near water and socket is overloaded.

58
Q

Describe and explain why it is dangerous to have frayed electric cord.

A

Frayed wiring can cause short circuit when two wires cut across/intercept and can give a person an electric shock.

Detailed explanation:
When the two wires, the live wire and the neutral wire intercepts it forms a parallel path for current to flow through where there is no resistance as compared to the other path through the light bulb/appliance that has appliance. This creates a short circuit that would overheat the wires in the parallel path with no resistance as more electrical energy is converted to heat energy and when the wires are overheated it will cause fire and also result in an electric shock if a person touches the wire as it creates another path for current to flow through.

59
Q

Describe and explain why it is dangerous to have an electrical appliance use near water.

A

On contact with faulty electrical appliances, water conducts electricity. A person can get an electric shock upon contact with water. This is because water usually isn’t pure and it contains ions that conducts electricity. Therefore, when a person with wet hands touches a damaged or faulty wire, it will form a parallel path and current would flow through the person’s body to the ground, causing the person to get an electric shock.

60
Q

What are some precautionary measures for frayed electric cord?

A

Replace frayed wires

61
Q

What are some precautionary measures for the situation where electrical appliance used near water?

A

Do not use electrical appliances in damp places.
Do not touch electrical appliances with wet hands. Turn off appliances before cleaning them.

62
Q

Describe and explain why it is dangerous to have socket being overloaded and the precautionary measures to be taken.

A

A large current will flow through the wires to the socket, and may start a fire. This is because when there is too much multi-plug and appliance, it will create more parallel path in the circuit and the total resistance in the circuit would decrease while the total current flowing through the circuit would increase.
P=IV
Power increases as current increases and this would cause excessive electric power to cause undesired thermal effects as electrical energy is converted to heat energy and causes the wires to melt and overheat, thus starting a fire.

Precautionary measures:
Don’t connect too many appliances or plugs to a single socket.
If need that convenience, switch off those that you do not need.

63
Q

Yellow and green wire:______
Blue wire:_______
Brown wire:______
State the names of the wire in these colours.

A

Yellow and green wire: Earth wire
Blue wire: Neutral wire
Brown wire: Live wire

64
Q

Explain how the earth wire protects a person when a live wire of an electric kettle becomes loose and is touching the metal casing.

A

The earth wire provides a path of low electrical resistance which allows very high current to flow from the live wire though itself to the ground, melting/blowing the fuse and/or tripping the circuit breaker and breaking the flow of current to the metal casing. The metal casing is no longer in contact with the live wire, so that it is no longer live. This prevents electrocution if a person touches the metal casing.

65
Q

What is a short circuit and why is it dangerous?

A

A short circuit is a circuit that allows most of the current to travel along a path of very low resistance, therefore negligible current goes through the intended load/resistor. It happens when an exposed live wire contacts the neutral wire or the earth wire. This causes a very larger current to flow through the wires (back to the source or to the ground). The wires may overheat and start a fire.

66
Q

What are two examples of a short circuit?

A

If appliance comes into contact with water and water touches both live and earth or live and neutral wire.

Frayed/damaged/ insulation causes live to come into contact with earth or neutral wire. neutral wire or earth wire to come into contact.

From slide in class:
E.g. Exposed wire comes in contract with neutral wire or grounded object.
E.g. Frayed/damaged insulation causes live and neutral wires to come into contact.

67
Q

In a household circuit, the switch is always connected to the live wire of an electrical appliance. Explain why this is safer than connecting the switch to the neutral wire.

A

If the live wire touches the metal casing during an electrical fault, no current will be flowing through the metal casing when the switch is off. Connecting the switch to the neutral wire will still allow the metal casing to be at high voltage and live even when the switch is off. This prevents the person from receiving an electric shock if he/she touches the metal casing.

68
Q

State one similarity and one difference between a fuse and a circuit breaker.

A

Similarity: Both are household safety devices that cuts off the power-supply to a circuit/appliance if the current exceeds a certain threshold value. (Overcurrent protection devices)

Differences: Fuses are one-use only/ used to be replaced after use, while circuit breakers can be reset after the fault is corrected.

69
Q

Why does some appliance not have any earth wire?

A

This is because the wires have double insulation to protect users from electric shock and it also uses non-metal casings

70
Q

What is a fuse?

A

A fuse consists of a short piece of thin wire, that heats up and melts when a large current flows through it.

71
Q

What are the common fuse ratings?

A

3A, 5A, 10A

72
Q

How do you decide on which fuse rating to use?

A

The recommended fuse rating to use is to round off the operating current to the nearest whole number, then +1A to that.

73
Q

What would happen if there is no fuse but there is an earth wire in a circuit?

A

If there is no fuse, there would be a close circuit and the metal casing would remain live as a large amount of current still passes through the circuit therefore when a person touches the metal casing the person would be electrocuted. However, if the person hasn’t touch the metal casing, it would still start a fire.

Main hazard: Fire due to overheating of wire
Side hazard: Electrocuted if person touches it

74
Q

If there is fuse but no earth wire in a circuit, what would happen?

A

If there is fuse but no earth wire, nothing would happen and it is an open circuit so when a person touches it, electric current flows through the person’s body and the person becomes a “earth wire”.
Main hazard: Person touches and connect two points of different hazard

75
Q

Describe briefly how the electric kettle works.

A

The heating element in an electric kettle has high resistance (relative to the rest of the circuit) and melting point so that it is able to heat up when an electric currents passes through it without melting. Electrical energy is converted to heat at the heating element.

76
Q

What is the function of the neutral wire?

A

The neutral wire which is connected at zero voltage to the main supply completes the circuit by providing a return path for the current to the main supply.

77
Q

What is the function of the live wire?

A

The live wire which is connected at high voltage to the main supply delivers current to the heating element of the kettle.

78
Q

During a malfunction such that the live wire is touching the metal casing of the kettle, state the current in the live wire, neutral wire an earth wire.

A

Current in Live wire: Infinitely high
Current in neutral wire: 0A
Current in wire Z: Infinitely high

79
Q

Explain why the current in the live wire will be infinitely high when the live wire touches the metal casing of the kettle.

Next, explain why the current in the earth wire will be infinitely high when the live wire touches the metal casing of the kettle.

A

This is because the metal casing has very low resistance, resulting in the current flowing through the live wire to be very high since V=RI.

The current flow from the live wire to the metal casing to the earth wire and since current remains the same in series, this results in the current in the earth wire to be infinitely high.

80
Q

What is brown, blue and green wire represent? Which side of the power socket?

A

Live wire (brown)
Neutral wire (blue)
Earth wire (yellow and green)
Live wire is plugged in to the right side
Neutral at the left
Earth wire in the middle

81
Q

Describe the flow of electron and current in a circuit.

A

Current flows from positive to negative and electron flows from negative to positive. Positive is the line that is longer and negative is the shorter one

Science Year 2 (12 decks)

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