Topic 2 Electricity Flashcards Preview

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Flashcards in Topic 2 Electricity Deck (45):
1

Current

The flow of electrical charge

2

What happens to the current in a single closed loop

The current is the same everywhere in the circuit

3

What pushes the charge around the circuit

Potential difference

4

What is resistance

Anything that slows the flow down

5

What does larger resistance mean for current

Current is smaller

6

What does total charge depend on

Current and time

7

Resistance in ohmic conductors

They have a constant resistance. The resistance doesn't change with current. At a constant temperature The current flowing through it is directly proportional to the Pd.

8

Filament bulbs

The resistance of filament bulbs change. When electrical charge goes through it some energy is transferred to thermal energy store. Resistance increases with temperature so as the current increases so does the heat and resistance

9

Diode

The resistance depends on the direction of the current. It allows current to flow in one direction but have a high resistant if it is reversed

10

LDR (light dependent resistors)

Is a resister that is dependent on intensity of light. In bright light the resistance falls. In darkness the resistance is highest. Applications are automatic night lights, outdoor lighting and burglar detectors

11

Thermistor

Is resister dependent on temperature. In hot conditions the resistance drops. In cool conditions the resistance goes up. They make good temperature detectors e.g. Car engines, temperature sensors and electronic thermostats

12

LDRs and Thermistors in sensing circuits

Sensing circuits are used to turn on or increase power to components depending on the conditions

13

What is a series circuit?

Is when complements are connected in a line from end to end. If a component is disconnected or broken the circuit is broken.

14

Potential difference in serious circuits

It is shared by components so the Pd around the circuit add up to the sieve Pd

15

Current in series circuits

The current is the same as all components

16

Resistance in a series circuits

The resistance adds up so more components makes a higher resistance

17

Cell potential difference in series circuits

Potential differences are added together if they are connected to same way so two 1.5V cells are in the same circuit the Pd supplied will be 3V

18

What are parallel circuits?

In parallel circuits the components are separately connected to the supply. Removing a component hardly affects the circuit. Things usually made from this

19

Potential difference in parallel circuits

The same across the components. All components get the source Pd

20

Current in parallel circuits

Current is shared between branches all the currents of the components equals the total current. The total current going into a junction must be equal to ten current leaving. If two identical components are connected in parallel then they have the same current

21

Adding a resistor in a parallel circuit

Reduces the total resistance.

22

AC (alternating current)

Mains supply is AC. AC's current is constantly changing by alternating into from positive to negative and back. AC supply in your home is about 230V average and 325V peak. The frequency of mains is 50Hz

23

DC (direct current)

Batteries supply DC. DC is always flowing in the same direction and it's created by direct voltage

24

Neutral wire

Blue wire completes the circuit and carries away current. Electricity flows in through the live wire and out through the neutral wire and is 0 V. Left wire

25

Live wire

Brown provides Alternating potential difference at an average of 230 V. Right wire

26

Earth wire

Green and Yellow for safety stops the casing from becoming live doesn't have a current unless there is a fault 0 V. middle wire

27

The wires

They have a core of copper and a coloured plastic the colour represents it's use

28

Live wires giving electric shocks

Your body is 0V so touching a live wire will cause 230V to pass through you and the current can injure or kill you. Can still happen even if it isn't on as long as there a connection between the live and earth it is a danger

29

The national grid

A giant system of transformers and cables to connect power stations to consumers.

30

Electricity production

They have to meet demand for the time of the day. They predict when the most electricity will be used when people get up and get back from work or school. Power stations run below their maximum capacity in case of shut downs of other stations. Lots of smaller power stations are ready to be started up quickly.

31

Pd and current in the national grid

It used a high Pd and low current. High current or Pd is needed for high power. Current is not viable as it losses lots of thermal energy through the wires. It is cheap to boost the Pd up to 400,000 V and keep current low.

32

Transformers

The step up transformers increase the Pd to 400,000V. The step down transformer brings the Pd down for safe usable levels.

33

Kettles transferring energy

Energy is transferred electrically from AC to thermal energy heating the inside of the kettle

34

Fan transferring energy

Transferred electrically from battery to kinetic energy stores in the fan's motor

35

Efficiency of electric appliances

The higher the current the more energy is transferred to the thermal energy stores so is more efficient

36

Potential difference

Energy transferred per charge passed

37

Build-up of static

Friction causes a a build-up of static. When certain insulating materials are rubbed together negatively charged electrons will be scraped off one and dumped on another. Leaving one negatively charged and the other positively charged. Example polythene negative and acetate positive when rubbed with a cloth duster

38

Movement of electrons

Only electrons move to form the positive or negative object

39

To much static

Too much static causes sparks. An electric charge builds up and the Pd increases and eventually the electrons can jump across the gap and cause sparks. It can also jump to any earthed conductor e.g. Getting an electric shock from a car.

40

Repelling and attraction

Like charges repel and opposites charges attract. The forces weaken as the distance increases. These forces cause the objects to move if the forces are strong enough this is known as electrostatics attraction or repulsion

41

Electric fields

Created around an electrically charged object. The. Loser the object the stronger the force.

42

Drawing electric fields

Electric field lines go from positive to negative. At a right angle to the surface. The closer the lines the stronger the field strength

43

Charged objects In an electric field

When a charged object is in an electric field it feels a force of attraction or repulsion. The force is caused by the electric fields interacting with each other. Increasing the distance decreases the strength of the forces between them

44

Drawing two oppositely charged particle

The two electric fields interact. Causes the forces to act on the two particles. These forces move the two particles closer together

45

Sparking explained by electric fields

Sparks are caused when there are is a big Pd between the charged object and the earth. High potential difference causes a strong electric field this causes electrons in the air particles to be removed. Air is normally an insulator but when it has been ionised it is more conductive so a current can pass through creating a spark