Section 20&21

Question 1

Energy transfers and systems

Answer 1

Can be transferred between stores mechanically (by a force doing work) electrically (by moving charge doing work) by heating or radiation

Question 2

Nine energy forms

Answer 2

Kinetic
Thermal
Chemical
Gravitational potential
Elastic potential
Electrostatic
Magnetic
Nuclear

Question 3

Work done

Answer 3

When a force moves and objects through a distance work is done on the object and energy is transferred

Question 4

Power

Answer 4

Power is how much work is done per second

Question 5

Forces

Answer 5

Interaction between objects cause forces
Interacting magnetic fields cause attraction or repulsion between magnetic objects – the electrostatic force causing this is due to interactions between the electrical fields

Question 6

What is a resultant force

Answer 6

A resultant force is the overall force on a point or object

Question 7

Forces and vector diagrams

Answer 7

An object is in equilibrium if forces on it are balanced – if all forces combined equal zero, its equilibrium

Use scale drawings to find resultant force – 1.draw all the forces acting on an object

2. Draw a straight line from start of first force to end of last force – this is the resultant force
3. measure length of resultant force to find magnitude and angle to show direction

Question 8

Current and circuits

Answer 8

Current is the flow of electrical charge
Potential difference (voltage) is the driving force that pushes the charge around
Resistance is anything that slows the flow down
Higher the potential difference, the higher the current

Question 9

Potential difference and resistance

Answer 9

Potential difference is the energy transferred per Coulomb of charge
Resistance increases with temp – when a current flows through a resistor, resistor heats up due to electrons colliding with ions in the lattice, it gives them energy so they vibrate heating it up

Question 10

Investigating components

Answer 10

You can investigate diodes, LDRS and thermistors
Ammeter and voltmeter measures current and Voltage

Variable resistor changes the current through circuits

Question 11

Circuit devices

Answer 11

The resistance of the thermistor decreases as temp increases
LDR – light dependent resistor, bright = falls, dark = highest
The I.V graphs show how the current varies as you change the potential difference

Question 12

Series and parallel circuit

Answer 12

Series circuits – different components connected in a line – Total potential difference of supply is shared between the components, total resistance of the circuit increases as you add resistance, the current is the same everywhere

Parallel – everything is independent – Each component is separately connected to positive and negative of the supply – Current is shared between branches – total resistance decreases if add second resistor

Question 13

Energy in circuits

Answer 13

Energy is transferred from cells and other sources – electrical appliances are designed to transfer energy to components in the circuit when a current flows
Heating up a component reduces its efficiency
Energy transferred depends on current potential difference and time

Question 14

Power in circuits

Answer 14

The total energy transferred depends on how long it’s on for and its power
Power also depends on current and potential difference

Question 15

Electricity in homes, fuses and earthing

Answer 15

Two types of electrical supply – alternating current(Charger constantly changing direction) – Direct current (charges move in the same direction)
Fuses are connected in the live wire
Earthing and fuses prevent electrical overloads

Blue wire = neutral
Brown wire = live (gives you an electric shock)
Green and yellow wire = earth wire