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Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

Electric charge can be

A

Positive or negative

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2
Q

An atom has the same number of electrons as protons

A

it is uncharged

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3
Q

What is a conductor and eg

A

Electrons flow through metals easily
Silver, gold, copper, steel

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4
Q

What is a insulator and eg

A

poor conductors of electricity
Eg: rubber, glass, plastic

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5
Q

Conduction in metals

A

Electrons are free to move around atoms
Under normal circumstances movement is random and there is no flow of charge
If a cell or battery is connected, the electrons move from the negative

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6
Q

What is current, unit, formula, and what do you measure it with

A

(Amperes)- rate or flow of charge
Current (A)= Charge (C) / Time (s)
Current is measured using an ammeter

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7
Q

Electric current flow

A

Flows from positive terminal to negative terminal

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8
Q

What is DC

A

Direct current (d.c)- Current flows in one direction (batteries)

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9
Q

What is AC

A

Alternating current (a.c)- Current constantly changes direction (mains supply)

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10
Q

What is Voltage, unit, formula, and what is used to measure it

A

(Volts)- also known as potential difference, electromotive force
The voltage across an electrical component is needed to make an electric current flow in it
Voltage (V) = Energy (J) / Charge (C)
Voltage is measured using a voltmeter

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11
Q

Characteristics of series circuit

A
  • Same current throughout the circuit
  • Voltage is shared between all the components
  • Total resistance is the sum of the individual resistances of each component
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12
Q

Characteristics of a parallel circuit

A
  • Voltage across each component is the same
  • Total current is the sum of the currents through the separate components
  • Every time another resistor is added in parallel, the total resistance decreases
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13
Q

Advantages of connecting 2 lamps in parallel instead of series

A
  • Lamps can be controlled individually
  • One lamp will continue working even if other does not
  • Lamps are brighter than when connected in series
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14
Q

What is resistance, unit, formula

A

(Ohms)- opposition that an electrical device has to the flow of current
Moving electrons can collide with the ions in the metal and this causes resistance as it is more difficult for the current to flow
If resistance increases, current decreases
Resistance (Ω) = Voltage (V) / Current (A)

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15
Q

In a wire, what would increase the resistance

A
  • Length of wire increases
  • Thickness of wire decreases
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16
Q

Relationship between heat of a metal and resistance

A

The hotter the metal gets, the higher its resistance
* When a current passes through a metal the metal gets hotter and the ions vibrate more
* This causes more resistance as it is harder for the ions to get past the electrons

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17
Q

What is Ohm’s law

A

Current is proportional to the voltage

18
Q

Current-voltage (I-V) graph for a resistor

A

Straight line through the origin
Obeys Ohm’s Law

19
Q

Current-voltage (I-V) graph for a Filament lamp

A

Resistance of a filament lamp increases as the temperature
Lamp doesn’t obey Ohm’s law

20
Q

Current-voltage (I-V) graph for a Diode

A

Current only flow through a diode in one direction
The diode has a very high resistance in the reverse direction

21
Q

Thermistor

A

Resistance of a thermistor decreases as the temperature increases

22
Q

Mains electricity

A

Electricity supplied to homes is called Mains Electricity
It is an alternating current supply
It has a frequency of 50 cycles per sec or 50 hertz

23
Q

three pin plug and what each colour represents in the electric cable

A
  • Live with brown insulation (carries current)
  • Neutral wire with blue insulation
  • Earth wire with yellow-green striped insulation
24
Q

What is the earth wire

A
  • Safety feature
  • Connected to the metal casing of a device
  • Other end of this wire is connected to a metal rod that goes to the ground
25
Q

What are the dangers of main electricity

A
  • Fire
  • Electrocution
26
Q

What is a fuse

A

Length of wire designed to melt and so breaking a circuit when the current passing through it goes above a certain level
The thicker the fuse the greater the current required to cause it to melt

27
Q

What is a circuit breaker

A

Electromagnetic device that breaks a circuit when the current goes above a certain value

28
Q

Comparison between circuit breaker and fuse

A

Fuses are simple and cheap to replace
Circuit breakers act more quickly than fuses and can be reset

29
Q

What is double insulation

A

Casings made from an insulator such as plastic rather than metal
Appliances will only have two-wire cables as they do not need the Earth wire

30
Q

Energy transferred

A

Energy transferred (J) = Voltage (V) * Current (A) * Time (s)

31
Q

Electrical power equations

A

Power (W) = Energy (J) / Time (s)
Power (W) = Voltage (V) * Current (A)

32
Q

What charge are protons and electrons

A

Protons are positively charged.
Electrons are negatively charged.

33
Q

what does charging by friction do

A

When insulating materials rub against each other, they may become electrically charged.
Electrons, which are negatively charged, may be ‘rubbed off’ one material and on to the other.
The material that gains electrons becomes negatively charged. The material that loses electrons is left with a positive charge

34
Q

What happens when a polyethene rod with a duster

A

Friction causes electrons to gain energy.
Electrons gain enough energy to leave the atom and ‘rub off’ onto the polythene rod.
the polythene rod has gained electrons, giving it a negative charge
the duster has lost electrons, giving it a positive charge
If the rod is swapped for a different material such as acetate, electrons are rubbed off the acetate and onto the duster.
the acetate rod has lost electrons, giving it a positive charge
the duster has gained electrons, giving it a negative charge
Both the rods and the duster are made of insulating materials. Insulators prevent the electrons from moving and the charge remains static.
Conductors, on the other hand, cannot hold the charge, as the electrons can move through them.

35
Q

How can you check if an object is positively charged

A

When a charged object is held close to a conductor, electrons in the conductor are able to move towards (or away from) the charged object
The attraction between the positive rod and the negative charges on the top surface of the paper will cause the paper to be attracted to the rod.

36
Q

Electrical forces

A

A charged object will experience non-contact force from another charged object.
The type of force will depend on the type of charge (positive or negative) on the two objects

37
Q

The properties of attraction and repulsion are often used to show that an object is charged in 3 examples

A

*a charged rod can pick up small pieces of paper
*a charged balloon can stick to the wall by attraction
*a charged rod can pull a stream of water towards it

38
Q

What is the law of charges

A

Like charges repel, unlike charges attract

39
Q

Uses of static electricity

A

Electrostatic precipitators
photocopiers
Ink jet printer
Paint spraying

40
Q

Problems with static electricity

A

*it is a nuisance when dust and dirt are attracted to insulators such as TV screens and computer monitors.
*it is a nuisance when clothes made from synthetic materials cling to each other and to the body, especially just after they’ve been in a tumble dryer

41
Q

Dangers of static electricity

A

Static electricity can build up in clouds. This can cause a huge spark to form between the ground and the cloud. This causes lightning –a flow of charge through the atmosphere.
It is dangerous when there are flammable gases or a high concentration of oxygen. A spark could ignite the gases and cause an explosion.
It is dangerous when you touch something with a large electric charge on it. The charge will flow through your body causing an electric shock. This could cause burns or even stop your heart. A person could die from an electric shock.
Refueling aircrafts and tankers also poses a particular danger. If the fuel passing along the hose to the vehicle was allowed to build up a static charge, a resulting spark might ignite the fuel. The hoses are earthed to stop this occurring.

42
Q

What is a golden leaf electroscope

A

The gold leaf electroscope has a very very thin piece of gold foil (called gold leaf) fixed at the top to a piece of copper.
The copper has a large round top, called the cap. The whole thing is put inside a glass case, to stop air blowing the delicate gold leaf around. The piece of copper goes through insulationin the top of the glass case, so that any charge on the gold leaf cannot escape.

Physics (7 decks)

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