PHYSICS P2

Question 1

Define current.

Answer 1

The rate of flow of charge.

Question 2

What does LDR and LED stand for?

Answer 2

LDR = Light dependant resistor
LED = Light emitting diode

Question 3

What is an electrical conductor?

Answer 3

A material that allows an electrical current to pass through it.

Question 4

What is static electricity?

Answer 4

When charge builds up on an object and then stays ‘static’ as there is nowhere for the charge to flow away.

Question 5

What is an electrical insulator?

Answer 5

A material that does not allow an electrical current to pass through it easily.

Question 6

What are the two things needed in a circuit that are needed to allow current to flow and for the circuit to work?

Answer 6

A power source and a complete circuit.

Question 7

What is charge?

Answer 7

A property of matter that experiences a force in an electrical field it can be positive or negative, it’s measured in coulombs (c). When charge moves, a current is created.

Question 8

Where does conventional current flow from?

Answer 8

Positive to negative.

Question 9

What is resistance?

Answer 9

Resistance is anything that will stop or slow down a current, it’s measured in ohms.

Question 10

What happens to the voltage, current and resistance in a parallel circuit?

Answer 10

The voltage stays the same across each branch and the current splits down each branch. Total resistance of circuit is reduced because current can take multiple paths.

Question 11

Take a few minutes to practice circuit symbols in the book.

Answer 11

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Question 12

What happens to the voltage, current and resistance in a series circuit?

Answer 12

Voltage is shared between the components and current is the same at any point. The total resistance of the circuit is the sum of the individual resistors.

Question 13

What is a thermistor and what are some of the applications of thermistors?

Answer 13

1. A resistor that changes its resistance when the temperature changes.
2. Household heating systems, Car engines

Question 14

What are some of the applications of LDR’s?

Answer 14

Automatic night lights and street lamps, some burglar alarms.

Question 15

Have a few minutes looking in the book and memorizing the differences between a ceramic resistor, a diode, and a filament lamp.

Answer 15

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Question 16

Describe what happens to the filament lamp when current is flowing through it?

Answer 16

As current increases, the atoms in the filament lamp begin to vibrate and this increases the temperature. This increases the resistance too which means there is less current for the same increase in potential difference.

Question 17

Describe what happens to a diode when there is current flowing through it?

Answer 17

A diode only allows current to flow in one direction. No current will flow if it’s pushed the wrong way as the diode’s resistance remains very large. When forward, the diode’s resistance is very large at low potential differences but when potential difference is higher, the resistance quickly drops and the current begins to flow.

Question 18

Describe what happens to a ceramic resistor when current flows through it?

Answer 18

Potential difference is directly proportional to the current, this relationship is called ohm’s law and is true as the resistance of the resistor is fixed and does not change.

Question 19

What is meant by an electric power?

Answer 19

Can also be defined as the rate of transfer of energy.

Question 20

If there is a higher power, what happens to the current?

Answer 20

A higher power means a greater current flows for a given period.

Question 21

What is meant by a direct current?

Answer 21

When the electron flow only flows in one direction. Car batteries, dry cells and solar cells all provide direct current.

Question 22

Electricity provided by a battery is known as what?

Answer 22

D.C. - Direct current, a typical battery has a voltage of 1.5 V.

Question 23

What is meant by an alternating current?

Answer 23

When the electron flow is constantly changing direction.

Question 24

What is the standard UK mains in terms of potential difference and direction of current flow?

Answer 24

Mains electricity is A.C. (alternating current) with a voltage of 230 V and a frequency of 50 Hz

Question 25

What are the colours of the live wire, earth wire and the neutral wire?

Answer 25

Live wire - Brown, provides current and 230 V Earth wire - Green and yellow, provides path for current to flow if there's a fault Neutral wire - Blue, Completes the circuit and carries away current

Question 26

Have a look at the graphs of D.C. and A.C. in the book?

Answer 26

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Question 27

What is a fuse?

Answer 27

A safety feature on a circuit that contains a wire which will melt if the current gets too high.

Question 28

Which directions do the three wires go in?

Answer 28

Brown goes right Blue goes left Green and yellow goes through the middle, at the top

Question 29

What happens when a charged object is placed into the field lines of another charged object?

Answer 29

A force is felt - either attraction or repulsion. The size of the force depends upon the strength of the electrical field.

Question 30

What is a uniform field?

Answer 30

The field between two parallel plates, one positive and the other negative.

Question 31

What happens when a jumper is rubbed against a balloon in terms of losing or gaining electrons?

Answer 31

The balloon gains electrons and become negatively charged and the jumper loses electrons becomes positively charged. As these objects have opposite charges, there is an attraction force between the jumper and the balloon.

Question 32

What happens if two insulators (two balloons) have like charges?

Answer 32

A repulsive force is felt - they repel eachother.

Question 33

What is the polarisation of electrical charge?

Answer 33

Positive ions are a lot more difficult to move on a charged object/wall. When a charged object, like a balloon, is moved close to a neutral object e.g. a wall, the electrons are repelled and move further into the object. This leaves an area of net positive charge on the surface, even though the object is electrically neutral overall, this causes an attractive force between the balloon and the wall.

Question 34

Why are series circuits useful?

Answer 34

They warn you if one of the components has failed. They also use less wiring than parallel circuits.

Question 35

Why are parallel circuits useful?

Answer 35

If a lamp breaks or a component is disconnected from one parallel wire, the components on different branches keep working. And, unlike a series circuit, the lamps stay bright if you add more lamps in parallel.

Question 36

What does a fixed resistor do?

Answer 36

A resistor that restricts or limits the flow of electrical current. Resistance doesn't change here.

Question 37

What does a variable resistor do?

Answer 37

A variable resistor is used to change the resistance in a circuit and is used to control switches and volume.

Question 38

What are diodes used for?

Answer 38

Used to convert an alternating current into a direct current.

Question 39

What is potential difference?

Answer 39

A measure of energy transferred between two points in a circuit.

Question 40

Google ' BBC Bitesize Alternating current and national grid' and learn the diagram of the national grid at the top of the page and learn diagram of transformers further down

Answer 40

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Question 41

What are transformers used for?

Answer 41

They are used to change voltages and currents in transmission lines. Step - down transformers - decreases potential difference but increases current Step - up transformers - increases potential difference but decreases current

Question 42

How is a transformer formed?

Answer 42

It's formed from two coils of wire around a magnetic core. The number of coils determines whether the transformers will step-up or step-down the voltage.

Question 43

How is the energy dissipated from pylons minimised?

Answer 43

- The cables are thick so that their resistance is low. - High voltages are used to reduce the current through the transmission lines.

Question 44

What is the national grid?

Answer 44

A system of cables, transformers and power stations.

Question 45

What is an electrical field?

Answer 45

A region where charges experience a force. The direction of the arrow shows the way a positive charge will be pushed.

Question 46

Where do field lines point to in a uniform field?

Answer 46

Away from the positive charges and towards the negative charges.

Question 47

Why does the ammeter have to have a resistance as close to 0 as possible?

Answer 47

If it was larger than 0, the current in the circuit would decrease and the ammeter wouldn't the read the correct amount of current flowing through the circuit.