PHYSICS PAPER 1

Systems - open and closed

Systems - open and closed

An object or group of objects

closed system= no energy added/can escape (doesn't exchange with surroundings)

open system= able to exchange energy and matter with surroundings

work done=

energy transferred

force * distance

energy stores

Thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic, nuclear

energy transfers

Mechanically, electrically, heating, radiation

heat transfers

conduction, convection, radiation

Convection

Process by which, in a fluid being heated, the warmer part of the mass will rise and the cooler portions will sink.

Conduction

Form of heat transfer where heat energy is directly transferred between molecules through molecular collisions or direct contact.

Radiation heat transfer

infrared waves

Kinetic energy equation

KE = 1/2mv^2

m, mass in kg

KE in Joules

v, velocity in m/s

elastic potential energy equation

U = 1/2 k e^2

U, joules

k, spring constant in N/m

e, extension in metres

Spring constant equation

force/extension

gravitational potential energy equation

GPE=mgh

m, mass in kg

g, gravitation field strength in N/kg (earth= 9.8)

h, height in metres

gravitational potential energy

Potential energy that depends on the height of an object

elastic potential energy

the energy of stretched or compressed objects

specific heat capacity

the energy required to raise the temperature of one gram of a substance by one degree Celsius

energy change= mass x specific heat capacity x temperature change

SHC measured J/kg degrees C

thermal conductivity

the measure of how good a material is at conducting heat

The higher the thermal conductivity of a material is the higher the rate of energy transfer via conduction across the material.

- the rate of cooling of a building is affected by the thickness and thermal conductivity of the walls

-metals are good conductors

-bad conductors are good insulators, like plastic and wood

Resistance

A material's opposition to the flow of electric current.

Ohm's Law

V=IR

p.d = current * resistance

the higher the resistance, the lower the current

- the higher the resistance of the component, the greater the share of p.d

-pd is directly proportional to current

Resistance in series

R = R1 + R2 + R3

Resistance in parallel

1/R = 1/R1 + 1/R2 + 1/R3

-resistance is lower as there is multiple paths for current to go down, goes down path of least resistance

-total resistance is smaller than smallest individual resistor

Diode

A device that permits current to flow through it in only one direction.

-acts as rectifier

-makes alternating current, direct current

resistance in graph

1/gradient

ohmic resistor IV graph

straight line through origin - gradient is constant

-show current and p.d. are directly proportional

non ohmic resistors

filament bulbs, diodes and L.E.D. they change resistance

- line is not straight

high current and resistance

- high current leads to more collisions with ions, causing the ions to vibrate harder, making them hotter

- this makes it harder for electrons to find their way through, increasing resistance

filament bulb

electric lamp consisting of a wire filament (usually tungsten) that emits light when heated, a non-ohmic device

-resistance increases as filament, where the current flows gets hot, making it harder for the electrons to pass though the vibrating tungsten ions, increasing resistance

thermistor

A resistor that changes its resistance with a change of temperature.

-usually decreases resistance when temp is increases

-eg, thermostat

light dependent resistor

An electrical component with a resistance that decreases as the light intensity incident on it increases

-non ohmic

-eg, automatic lights

specific latent heat

Amount of heat needed to change the state of 1 kilo of a substance WITHOUT a change in temperature.

E=mL

m, mass in kg

energy in joules

L, SLH measured in J/kg

why is the specific latent heat of vaporisation greater than that of fusion?

in fusion the intermolecular bond must only weaken, in vaporisation they are completely broken

cooling curve

a diagram that illustrates temperature changes and changes of state for a substance as heat is removed

mains electricity

An a.c supply, which in the UK has a frequency of 50Hz a value of 230V.

conservation of mass

the principle stating that matter is not created or destroyed during a chemical reaction/change of state

Wires in a plug

Blue wire=neutral

Brown wire=live

Green and yellow stripes=earth

live wire in plug

the wire that is connected to 230 V

neutral wire in plug

Completes the circuit - p.d. 0V

earth wire

a wire through which current only flows when there is a leak of current in an appliance; it is coated in yellow and green plastic

-grounds current so appliance does not go live

density

mass/volume

particle model of matter

model that explains the behaviour of solids, liquids, and gases; it states that all matter is made up of tiny moving particles that attract each other and have spaces between them

internal energy

kinetic energy + potential energy

aka thermal energy

fuse

A safety device with a thin metal strip that will melt if too much current passes through a circuit

physical change

A change in a substance that does not involve a change in the identity of the substance

why cant a substance change state and temperature at the same time?

because a change in potential energy cannot happen at the same time as a change in kinetic

energy resources

Renewable (sun, sea, wind) or non-renewable (coal mine, gas well, oil well) resource used for obtaining an energy source.

what p.d to power stations produce electricity at

25000V

energy store changes when a moving object hits an obstacle

The object's energy is in the kinetic store at the start because it is moving.

When the object collides with the obstacle, energy is converted to:

The kinetic store of the obstacle (making it move),

The thermal store of the object and the obstacle (the particles in the object and the obstacle vibrate more).

Some energy remains in the object's kinetic store as it moves away after the collision.

energy conversion when object projected upwards

The object's energy is initially in the kinetic store as it moves upwards.

The object's energy is slowly transferred from the kinetic store to the gravitational potential store as it slows down and climbs higher.

Once the object reaches its highest point, all of its energy is in the gravitational potential store.

As the object falls again, energy transfers from the gravitational potential store to the kinetic store.

energy conversion when object accelerated by constant force

Work is done by a force on an object. This work is converted to the object's kinetic store.

energy conversion when a vehicle slows down

To begin with, the vehicle's energy is in the kinetic store. The brakes do work slowing the car down. During this process, energy is dissipated (lost) through heat and sound.

energy conversion when bringing water to boil in an electric kettle

Energy transfers from the electrical store of the mains power supply to the thermal store of the water.

energy

force * distance

E=QV

energy= current* charge

E=pt

energy= power*time

Work done when a current flows

current x charge

Power definition

The rate at which energy is transferred or the rate at which work is done

eg, two electric motors that both lift the same weight through the same height, but one does it much faster than the other= more powerful

conservation of energy

Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed

-there can be energy transfers within a closed system, but there is no net change of energy

switch

a device that opens or closes a circuit

cell

battery

A device that converts chemical energy to electrical energy

-more than 1 cell

diode

A device that permits current to flow through it in only one direction.

-extremely high resistance until certain positive p.d

resistor

An electrical device that resists the flow of electrical current

Variable resistor

A resistor whose value can be varied between its minimum and maximum values.

Light Emitting Diode (LED)

A diode that will produce light when current flows through it.

lamp

light source

fuse - symbol

voltmeter

A device used to measure voltage, or electrical potential energy difference

-in parallel

ammeter

a device used to measure current

-in series

Thermistor symbol

A resistor that changes its resistance with a change of temperature.

LDR (Light Dependent Resistor)

A resistor which has lower resistance if light is shining on it more brightly.

For electrical charge to flow through a closed circuit

the circuit must include a source of potential difference

step up transformer

increases the voltage

step down transformer

decreases the voltage

current

flows through a wire some energy is lost as heat

power stations

power stations produce electricity at 25,000 v

power lines

Electricity is sent through these at 400,000v

household voltage

the voltage of household electricity is about 230v

Ohm's law

V=IR

Power 1

Energy transferred / time

Power 2

I^2xR

Charge

Q=It

power

P=IV

energy

E=QV

Resistance of a wire

resistance is directly proportional to length

IV characteristics of a diode

Current only flows in one direction, with a very high resistance in the reverse direction - non ohmic

IV characteristic of a filament lamp

Non-Ohmic. Behaves in the same way regardless of polarity.

IV characteristic of fixed resistor

I is directly proportional to V

LDR

a light dependent resistor, a resistor whose value of resistance can change as the intensity of the light falling on it changes

Fixed Resistor

Resistors that have a value that cannot be changed.

Thermistor

A resistor that changes its resistance with a change of temperature.

Variable resistor

A resistor whose value can be varied between its minimum and maximum values.

Fuse

A safety device with a thin metal strip that will melt if too much current passes through a circuit

3A 5A 13A

Law of Attraction

This law states that oppositely charged objects will exert an attractive force on each other while two objects that have like charges will repel each other. The attractive force varies with the size of the charges as well as the distance between them.

To get more readings for IV graph

Use variable resistor, add more cells

direction of current flow

assume in exams that current flows from + to - , which is usually anti-clockwise, useful for diode questions

Rectifier

Apparatus that changes alternating current to direct current

Diodes act as rectifies as they block alternating current when it changes direction.

Gradient of IV graph

1/resistance

Cells in series

Vtotal= V1 + V2 + V3

advantages of putting lights in parallel

- each bulb can be individually turned off

- if one bulb breaks, current will still flow through other branches

Current def

Rate of flow of charge symbol -I Measured in A

Resistance def

Rate of flow of electrons of a material Measured in ohms

Voltage def

Amount of energy given to each charge

series circuit current

Current is the same everywhere