IGCSE🤍

newton’s first law

an object at rest will remain this way unless it’s acted upon by an external force

newton’s second law

a net force causes an object to accelerate in the direction of the net force (the harder someone pushes me the faster I’ll move)

What’s the formula of force?

Force (newtons) = Mass (kg) x Acceleration (n/kg) {F = M x A}

inertia

a measure of how difficult it is to change velocity

What is the formula of inertia?

Inertia = Force / Acceleration

newton’s third law

when two objects interact they exert an equal and opposite force on each other

what are the equations of notion?

S displacement

U initial velocity

V final velocity

A acceleration

T time

what does Hooke’s Law state?

the extension object is proportional to the force applied (springs, extensions and elasticity)

deformation

when a force may produce a change in size and shape of a body

elastic deformation

the object returns to its original shape

plastic deformation

the object does not return to its original shape

elastic limit

when an object is stretched out to a point where it cannot return to its original shape

what is the formula of Hooke’s Law?

F = kx or F = K x E

F is the force applied to the spring in Newtons

k is the spring constant in Nm -1

z or E is the extension in meters (m)

energy

the ability to do work

• cannot be created or destroyed

• 8 types of energy

• it can be stored or transferred from one form to the another

• measured in Joules (J)

gravitational potential energy

• any object in a gravitational field has a gravitational potential energy due to its position in that filed

  • depends on the distance between 2 objects

what is the formula for the gravitational potential energy?

GPE (joules) = weight (newtons) x height (meters)

GPE = mass (kg) x gravitational field strength (newtons per kilogram {Nkg-1}) x height (meters)

what is the formula for work?

work done = force x distance

what is the formula for power?

power = energy / time = power = work / time

• unit of power: WATTS

conduction

the movement of heat through a solid

convenction

the movement of heat in a fluid

radiation

the emission of energy as electromagnetic waves

thinking distance

the distance the car travels in split second between a hazard appearing and the driver applying the brakes

braking distance

the distance the car travels during its deceleration whilst the brakes are being applied

what are the main effects of both thinking and breaking distance?

Thinking distance:

• How fast you are going

• Being wide awake (tiredness, drugs, carelessness, alcohol, old age)

• Visibility- rain, on going lights, fog and the night

Braking distance:

• How fast you are going

• The mass (or load) of the vehicle

• If the car is poorly maintained (brakes & tires)

• The grip of the road surface - on a wet road you can skid twice as long

what are the different types of energy?

• Electrical

• Light

• Sound

• KInetic

• Thermal

• Gravitational

• Elastic

• Chemical

kinetic energy

anything which moves

(example: running)

gravitational

anything above the ground has gravitational potential energy

efficiency

useful energy transferred by the device (J)

what is the formula for efficiency?

energy supplied = useful energy delivered + wasted energy

density

the mass of a substance per unit volume

• usually expressed in g/cm ³

What is the formula for density?

density = mass / volume

• mass = density x volume

• volume = mass / density

what is the formula for pressure?

pressure = force / area

• Force is measured in Newtons (N)

• Area is measured in meters squared (m²)

• The unit of pressure is Newtons per second meter (N/m²)

what is the formula for sankey diagrams?

output / total input x 100

how is electricity transported from the source to your home? (formula)

power station → transmission lines → home

electrical circuit

a closed loop that allows electric current to flow from a power source, through various components and back to the power source

What are the parts of a plug ?

earth wire: protects the user if there is a fault

live wire: electrical energy travels through this wire to the appliance

neutral wire: completes the circuit

socket: the insert for the plug

conductors

allows transports of electricity

(example: copper)

what’s the role of a conductor?

make the device/appliance work

insulators

doesn’t allow transport of electricity

(example: plastics)

what is the role of insulators?

protect users from getting electrocuted

current rating

level of current, if electricity power surges or deliver overcurrents (“goes over current rating”), the fuse burns out or breakers turn off

what are conditions needed for appliance with metal casting?

• to have an earth wire connected to casting and ground

• needs to drain electricity to the ground for protection if there’s a damage on the circuit and accidentally connects the wire to casting

  • this is dangerous

what’s the role of appliance switches?

connects and disconnects device to main electrical circuit

electrical resistance

the opposition to flow of electric current, electrical energy is converted to heat or/and light

what is the formula for electrical power?

• the higher the electrical power, the brighter the light produced

• energy input / used per unit time (Js = W)

what’s the formula for electrical current?

power {P} (watts) = current {I} (c/s) x voltage {V} (J/c)

what’s the formula for electrical energy?

Power {P} = Electricity energy used {E} (joules) / Time duration {T} (sec)

voltage

“potential difference”

this is what drives the current to flow

• pushes charges to flow

cathode - anode, which one is positive and which one is negative?

• cathode is a POSITIVE charge

• anode is a NEGATIVE change

  • the diagram shoes Fleming’s right hand rule

ammeter

a device that measures current in a circuit

what are the properties of a ammeter?

• connected in series with the component

• has very low resistance it will have no effect on the current on the circuit

• it measures the amount of charges passing per unit time (Q/t)

voltmeter

a device that measures voltage in a circuit

what are the properties of a voltmeter?

• connected in parallel with the component

• has very low resistance it will have no effect on current on the circuit

• measures the amount of energy transferred to a coulomb of charge

circuit diagram

simplified pictorial representation of an electrical circuit where in electrical components are represented by circuit symbols

• used to easily see the connectivity of electrical compounds

• easy to draw

What’s the function of each part of a plug?

earth wire: provides a path for electric current to flow from the casting of the appliance to the ground

live wire: carries to the alternating potential difference of 230V from the supply

neutral wire: completes the circuit

fuse: designed to melt and break the circuit if the current flowing through it exceeds its rating

cable grip: holds cable tightly in place so that wires don’t become loose and touching the external castings

what will happen if a surge of current flows a fuse?

it will melt and the circuit will be broken

• if fuse is said to have blown, would then need to be replaced

what is the role of circuit breakers?

switches on circuit breakers are driven by electromagnets

• detects surges in current

  • when detected, a switch is opened, immediately breaking the circuit

• can be reset by clicking the switch back to its original position

• makes them much more convenient than fuses

resistor

an electrical component that resists the flow of an electric current

how does a electrical fault develops?

electrical fault develops → surge of current through earth wire → fuse melts, isolating appliance from live → appliance safe

what are fuses and circuits designed to do?

cut off the flow of electricity to the appliance

• only occur of a surge of electricity flows through the appliance

what is the resistors used for?

to limit the amount of current that flows through a circuit

Ohm’s law (Ω)

as the resistance of circuit increases, the current will decreases

• as temperature increases, resistance also increases

what is power in physics?

when work is done on a object, energy is transferred. The rate at which this energy is transferred is called power. So the more powerful a device is , the more energy it will transfer each second

power

amount of energy that is transferred per second

• measured in joules per second or watts (W)

• devices that transfer lots of energy are measured in kilowatts (kW)

what does the power of an appliance (P)?

• Energy (joules) {E} = Power (watts) {P} x Time (seconds) {t}

how much energy it transfer each second

• meaning total energy (E) transferred by an appliance is equal to its power multiplied by the length of time (in seconds) the appliance is being used

how would direct current appear on a voltage-time graph?

a straight horizontal line at a constant voltage

how would alternating current appear on voltage-time graph?

a curve alternating between positive and negative voltages

• the positive and negative values indicate the direction of current flow

what are the main differences between alternating and direct current?

alternating current changes direction, while direct current flows in one direction

step down transformer

decreases the potential difference of the electricity transported through the transmission cables to around 230V, making it safe for domestic use

step-up transformer

increases the potential difference of the electricity produced in this generator to around 400 000V

• this allows the same electrical power to be transferred at a lower current

  • means electricity can be transmitted along the cables of the National Grid MORE EFFICIENCY because less energy is dissipated as heat

pylon

tall structures which carry high-voltage transmission cables above the ground

what is the generator effect?

when energy is transferred from the kinetic energy store of the moving turbine to induce an electric current

What are the properties of the national grid?

• The power station is fueled to power generators

• The generators produced electricity

• Electricity is transmitted to a step-up transformer

• The voltage is increased to 400 000V

• Electricity is transmitted through overhead cables on pylons

• Electricity is transmitted to a step-down transformer

• The voltage is decreased to 230V

• Electricity is supplied to consumers in their homes at a safe voltage

what causes a transfer in energy?

the work you do because to apply a force you need to move something

• the work done by a force depends on the size of the force and the distance moved

what’s the formula for work done?

work done (joules) = force applied (newtons) x distance moved in the direction of the force (meters) {energy transferred = work done}

what does work done overcome ?

friction is transferred as energy that heats the objects that rub together and heats the surroundings

• the power of an appliance in measured in watts (w)

what’s the formula for power?

Power (watts,w) = work done (joules, J) / time taken (sec, s) = useful energy transferred (Joules, J) / time taken (sec,s)

gravitational potential energy

energy stored in an object because of its position in the Earth’s gravitational field

• when you lift an object up, some muscles transfer chemical energy from the muscles into gravitational potential energy of the object

What are the properties of gravitational potential energy?

• the upward force you need to apply to it is equal to the object’s weight

  • when an object is moved up, its gravitational potential energy increases

  • when an object is moved down, its gravitational potential energy decreases

The work done when an object moves or down depends on, what?

1) how far it is moved vertically (its change of height)

2) its weight

what’s the formula for the change of gravitational potential energy?

• change of gravitational potential energy (J) = weight (N) x change of height (m)

• change of gravitational potential energy (J) = mass (kg) x gravitational field strength (N/kg) x change of height 9m0

What is the main properties of energy?

• energy CANNOT be created or destroyed

What’s the formula for kinetic energy?

kinetic energy (joules) = ½ x mass (kg) x speed² (m/s²)

elastic potential energy

the energy stored in an elastic object when work is done on it to change its shape (example: when you stretch a rubber band the work you do its stored in it as elastic potential energy)

wasted energy

dissipated (spreads out) to the surroundings

useful energy

eventually transfers to the surroundings too

• energy is less useful the more it spreads out

how can you represent any transfer in which energy is wasted?

sankey diagram

what’s the formula for input energy?

input energy (energy supplied) = useful energy transferred + energy wasted

what’s the formula for efficiency?

efficiency = useful power out / total power in x 100 %

what is THE property of energy?

it CANNOT be created or destroyed

exothermic

transfer energy from the reacting chemicals to their surroundings

what’s an example of exothermic reactions?

the burning of fuels such as combusion of methane gas

what happens when methane burns?

when methane (the main gas present in natural gas) burns, it gets oxidised and releases energy to its surroundings

what is another example of exothermic reactions?

netralisation

how can you measure the rise in the temperature?

• by using simple apparatus

• the products of exothermic reactions have a lower energy content than reactants

what is used to measure the differences in energy?

kilojoules per mole (kJ/mol)n

endothermic

transfer energy from the surroundings to the reacting chemicals

what is an example of endothermic reactions?

• decomposition of calcium carbonate

  • thermal decomposition reaction

what happens to the decomposition of calcium carbonate?

• when heated, it forms calcium oxide and carbon dioxide. This reaction only takes place if you keep heating the calcium carbonate strongly

• the calcium carbonate needs to absorb energy from the surroundings

• the products have a higher energy content than the reactants

what can exothermic changes be used for?

they can be used in hand warmers and self-heating cans