Electricity

Question 1

Electric charge can be

Answer 1

Positive or negative

Question 2

An atom has the same number of electrons as protons

Answer 2

it is uncharged

Question 3

What is a conductor and eg

Answer 3

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

Question 4

What is a insulator and eg

Answer 4

poor conductors of electricity
Eg: rubber, glass, plastic

Question 5

Conduction in metals

Answer 5

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

Question 6

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

Answer 6

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

Question 7

Electric current flow

Answer 7

Flows from positive terminal to negative terminal

Question 8

What is DC

Answer 8

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

Question 9

What is AC

Answer 9

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

Question 10

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

Answer 10

(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

Question 11

Characteristics of series circuit

Answer 11

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

Question 12

Characteristics of a parallel circuit

Answer 12

• 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

Question 13

Advantages of connecting 2 lamps in parallel instead of series

Answer 13

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

Question 14

What is resistance, unit, formula

Answer 14

(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)

Question 15

In a wire, what would increase the resistance

Answer 15

• Length of wire increases
• Thickness of wire decreases

Question 16

Relationship between heat of a metal and resistance

Answer 16

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

Question 17

What is Ohm’s law

Answer 17

Current is proportional to the voltage

Question 18

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

Answer 18

Straight line through the origin
Obeys Ohm’s Law

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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

Question 21

Thermistor

Answer 21

Resistance of a thermistor decreases as the temperature increases

Question 22

Mains electricity

Answer 22

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

Question 23

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

Answer 23

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

Question 24

What is the earth wire

Answer 24

• 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

Question 25

What are the dangers of main electricity

Answer 25

* Fire * Electrocution

Question 26

What is a fuse

Answer 26

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

Question 27

What is a circuit breaker

Answer 27

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

Question 28

Comparison between circuit breaker and fuse

Answer 28

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

Question 29

What is double insulation

Answer 29

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

Question 30

Energy transferred

Answer 30

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

Question 31

Electrical power equations

Answer 31

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

Question 32

What charge are protons and electrons

Answer 32

Protons are positively charged. Electrons are negatively charged.

Question 33

what does charging by friction do

Answer 33

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

Question 34

What happens when a polyethene rod with a duster

Answer 34

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.

Question 35

How can you check if an object is positively charged

Answer 35

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.

Question 36

Electrical forces

Answer 36

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

Question 37

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

Answer 37

*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

Question 38

What is the law of charges

Answer 38

Like charges repel, unlike charges attract

Question 39

Uses of static electricity

Answer 39

Electrostatic precipitators photocopiers Ink jet printer Paint spraying

Question 40

Problems with static electricity

Answer 40

*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

Question 41

Dangers of static electricity

Answer 41

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.

Question 42

What is a golden leaf electroscope

Answer 42

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.