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iGCSE Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

In a cell which side is the positive terminal?

A

Left side.

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2
Q

An atom contains two types of charged particles

A

-Proton (+1)
-Electron (-1)

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3
Q

What are the differences between series and parallel circuits in regards to current and voltage?

A

Series:
-Same current flows throughout
-Voltage is not the same. Total is equal to the sum of potential differences across each component
Parallel:
-Current flowing in a junction is equal to the current leaving it.
-The sum of the currents in each section is equal to the total curent
-The voltage across each branch is the same

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4
Q

Where must a voltmeter be placed in a circuit?

A

In parallel to the component that is being measured.

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5
Q

Give an equation linking voltage, energy transferred, and charge.

A

V=E/Q
E/V x Q

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6
Q

A volt can also be describes as a…

A

Joule per coulomb

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7
Q

What is current

A

The rate of flow of charge in a certain amount of time

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8
Q

What is an ammeter and where must it be connected in a circuit?

A

Measures current. It is places in a series with the component it is required to measured.

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9
Q

Equation including time, current and charge

A

Q = I x T
Q/IT
Q=Charge (coulombs)
T=Time (s)
I= Current (amps)

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10
Q

State the equation linking current, voltage, resistance with their units.

A

V=I x R
V/IR

I=Current (amps)
R=Resistance (Ohms)

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11
Q

How does changing the resistance in a circuit change the current?

A

-Current is inversely proportional to resistance. Therefore at a constant voltage, increasing the resistance will decrease the current.
-In an electrical circuit the flow of electrons causes a current. A high resistance makes it harder for electrons to pass through and therefore reduces the current.

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12
Q

How can you use a variable resistor to increase the current in a series circuit?

A

You set the variable resistor to have a lower resistance, this should increase the current

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13
Q

Explain why when two resistors are in series the overall resistance increases

A

-Current in each of them is the same I1=12=1T
-Total voltage=The sum of the voltage across each resistor.
Therefore as V1=IT X R1 and V2=I2 X R2 then VT= (IT X R1)+(IT X R2) which can be written as VT=IT(R1+R2). Also VT=IT X RT
Therefore RT=R1 + R2
Therefore the overall resistance increases as you add resistors in series.

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14
Q

Why does the net resistance of two resistors in parallel decrease?

A

In parallel:
-IT=I1+I2+I3
-V1=V2=V3
Therefore 1/RT=1/R1+1/R2+1/R3

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15
Q

Explain the relationship between voltage, current and resistance in a filament lamp.

A

As temperature increases in the lamp the resistance also increases. This is because a higher temperature makes the ions in the filament vibrate more, making it harder for electrons to pass through. This therefore decreases the current. If voltage is doubled, current will not be doubled.

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16
Q

How do diodes work?

A

A diode only allows current to flow in one direction. If current is flowing in the right way, the resistance is large at small voltages, but ay higher voltages the resistance becames very small.

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17
Q

Describe the relationship between thermistors and resistance.

A

The resistance of a thermistor changes with temperature, when the temperature increases the resistance decreases.

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18
Q

How does a Light Dependent Resistor work?

A

The resistance of a LDR varies with light. As the light intensity increases, the resistance decreases.

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19
Q

When an electrical current flows through a resistor why does it light up?

A

There are collisions between the electrons and the ions in the resistor’s lattice. This causes a transfer of kinetic energy into thermal energy which is released into the surroundings.

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20
Q

How do low resistance wires reduce unwanted energy transfers?

A

A smaller resistance will mean there are fewer collisions, therefore less energy will be wasted through heating.

21
Q

What are some advantages and disadvantages of the heating effect?

A

Advantages:
-Can be used for appliances such as toasters or electrical fires, where the hot wire helps heat the bread or room
Disadvantages:
-The loss of energy as heat energy can make an appliance inefficient
-If an appliance overheats it can catch fire or overheat, which could ruin the device or injure the user

22
Q

State the equation linking electrical energy tranferred, voltage, current and time.

A

E=I x V x T

23
Q

The energy tranferred per second is also known as…

A

Power (in Watts)

24
Q

State an equation linking electrical power, current and voltage.

A

P = I x V
P/IV

25
Q

State an equation for power in terms of current and resistance

A

P= I² x R
P/I²R

26
Q

Define direct current

A

Current flows in only one direction

27
Q

Define alternating current

A

Direction of current changes continuously as time passes.

28
Q

What type of current do batteries supply?

A

Direct Current

29
Q

What is the difference between the function of the live and the neutral wires?

A

Live: supplies the voltage to the circuit and forms the current.
Neutral: Carry the current away from the appliance. Completes the circuit so that the current can flow.

30
Q

How does an earth wire ensure safety?

A

The earth wire is connected to the metal casing of the device and provides a low resistance path to the ground. Therefore if a fault occurs the earth wire allows the large currents in the live wire to flow through to the ground.

31
Q

Colour of the live wire

A

Brown or red

32
Q

Colour of the neutral wire

A

blue

33
Q

Colour of the earth wire

A

Green and Yellow

34
Q

How does a fuse stop the device from getting damaged.

A

When a fault occurs and there is an excess current flow, fuse melts (blows), and disconnects the live wire. Current must be greater than fuse rating for fuse to blow.

35
Q

Why is it important to connect a fuse or switch to the live wire.

A

When the switch is turned off, or when the fuse breaks, it will break the circuit and stop current running through the wire since live wire carries the voltage. This provides a method to stop current from flowing into the appliance.

36
Q

Define double insulation

A

When casing of an appliance is made of plastic, as it is an insulator and doesn’t let electricity pass through.

37
Q

3 advantages of circuit breakers over fuses.

A

-More sensitive.
-Easier to reset.
-Doen’t need to be replaced.

38
Q

Which connection is not required when the appliance is double insulated?

A

Earth Wire is not required. Because earth wire is connected to the casing of the material. If casing is made out of plastic (insulator), earth wire will not be able to let the current flow to the ground

39
Q

How does an insulator build static charge?

A

-When two insulators are rubbed together, friction causes negatively charged particles (electrons), to be transferred from one material to the other.
-The material that loses electrons becomes positively charged since there are fewer negative than positive particles.
-The one that gains electrons becomes negatively charged.
-Their charges are equal but opposite, since they lose/gain an equal amount of electrons.

40
Q

How do opposite charges interact?

A

The charged objects are attracted to each other, ie. a proton and electron will attract
So a negatively charged object attracts a positively charged object (vice verse since Newton’s 3rd Law)

41
Q

How do like charges interact?

A

Like charges objects repel eachother

42
Q

Why do we feel an electric shock?

A

-When an object builds up an electrostatic charge, it needs to be earthed via a conductor
-So that either excess electrons can flow to the earth electrons can flow from the earth into the object to even out the charge.
-Discharge when experienced by humans is also known as electric shock
-Can also happen if you touch a charged object which you are earthed.

43
Q

Why does lightning occur?

A

-Clouds can build up electrostatic charge due to friction
-When this charge become large enough the clouds discharge via the air to the earth
-Lightning

44
Q

Why does a balloon stick to a wall?

A

For a positively charged ballon, when placed next to a wall, the positive charges inside the wall get repelled to the other parts of the wall. This leaves an area of the wall with a negative charge, which attracts the positively charged balloon towards the wall.

45
Q

How can a comb be used to pick up paper pieces?

A

A comb can be rubbed against an insulator, causing it to pick up an electrostatic charge, due to the transfer of electrons. The charged comb repels the like-charged particles in the neutral paper, leaving the oppositely charged particles closest to the comb. This end of the paper is then attracted to the comb.

46
Q

How does earthing remove excess charge?

A

It provides a path with a low resistance for the electrons to flow either from the device or towards the device to reduce the charge build up.

47
Q

How are electrostatic charges used in everyday situations to prevent dangerous build-up?

A

Paint spray is electrostatically charged, meaning when it is sprayed it will attract to the object. Similarly, as each paint particle has the same charge, they will repel each other meaning the paint will spread out. This means that less paint is wasted.

48
Q

How does static electricity cause danger when fuelling cars?

A

-Static charge can build up due to the friction between the pipes and the fuel flow
-When the charge builds up, a spark may be discharged
-The spark could start a fire id it reacts with the flammable fuel
-This is resolved by earthing the vehicle and pump

iGCSE Physics (8 decks)

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