Study your flashcards anywhere!

Download the official Cram app for free >

  • Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

How to study your flashcards.

Right/Left arrow keys: Navigate between flashcards.right arrow keyleft arrow key

Up/Down arrow keys: Flip the card between the front and back.down keyup key

H key: Show hint (3rd side).h key

A key: Read text to speech.a key

image

Play button

image

Play button

image

Progress

1/150

Click to flip

150 Cards in this Set

  • Front
  • Back

Forces act in

Forced act in pairs.

When a force acts in one direction

an equal and opposite force is exerted in other direction

what is a reaction force?

When 2 forces interact they are equal and opposite in direction e.g. a person exerts a force on the chair but the chair applies an equal force upwards on the person, a reaction force.

Weight is a

force measured in newtons.

weight and mass

Don’t confuse mass and weight as mass is actually the amount of ‘stuff’ that makes up an object measured in kilograms.

The equation to work out weight is...

Weight is the force calculated by Weight (N) = Mass (kg) x Gravitational field strength (N/kg)

The gravitational field strength of earth is

The gravitational field strength on Earth is taken as 10N/kg.

The speed of an object is

distance travelled in seconds

The gradient of a line on a distance time graph represents

speed

On a distance time graph, the greater the gradient of line

the greater the speed

On a distance time graph if the line is horizontal

the object is stationary

On a distance time graph, if the object is moving at a constant speed the line is

a straight line sloping upwards

How do we calculate the speed of an object?

speed (m/s)= distance traveled (m)


-------------------------------


Time taken in (s)

Velocity is

speed in a given direction

If an object changes direction...

it changes velocity even if the speed remains the same

Therefore if the velocity of an object changes

it accelerates

Acceleration=

a (m/s2)= v-u


-------


t




where v is the final velocity, u is the initial velocity and t is the time

The gradient of the line on a velocity time graph represents

acceleration

The steeper the gradient of a velocity time graph

the greater the speed

if the line on a velocity time graph is horizontal the object is

travelling at a steady speed so the acceleration is zero

The distance travelled by an object is given by

the area under the line of its velocity time graph

What is the resultant force?

single force that would have the same effect on the object as all the original forces acting together.

When the resultant force of an object is zero...

if object is at rest it will stay at rest


if the object is moving it will carry on moving at the same speed in the same direction

when the resultant force of an object is not zero,

there will be acceleration in the direction of the force

if the resultant force is not zero the object will,

accelerate in the direction of the resultant force if it was at rest


if object is moving in same direction of resultant force it will accelerate in that direction


if object is moving in opposite direction of resultant force it will decelerate

A resultant force always causes an

acceleration

Acceleration is the change in velocity

an object can accelerate by changing =its direction even if it is going at a constant speed. so a resultant force is needed to make the object change direction

resultant force is found by

f=m x a




f= force (N)


m= mass(kg)


a=acceleration (m/s2)

What is the stopping distance?

the distance traveled during the drivers reaction time plus the distance it travels under the braking force


Stopping distance = thinking distance + braking distance

thinking distance is increased

if driver is tired or under influence of drugs or alcohol

Balanced forces occur when

an object is stationary or moving at a constant speed. The faster an object is moving the bigger the frictional forces acting on it.

Braking distance can be increased by

poorly maintained roads or bad weather conditions


condition of car i.e if the brakes or tyres of car are worn

An object falling through a fluid or gas will initially accelerate due to the force of gravity as

there is a resultant force acting on it which is gravity

The force of gravity can be referred to as

weight

to work out the weight you do

w= m x g


where w is the weight (N) as it is the force


m is the mass (kg)


g is the acceleration due to gravity (m/s2)



When an object falls through a fluid,

the fluid exerts a drag force on the object


resisting its motion

in a fluid, the faster the object falls

the bigger the drag force becomes until eventually it will equal the weight of the object.


resultant force is now zero so the body stops accelerating. It moves at a constant speed called Terminal velocity

What is terminal velocity?

The constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration.

what is the extension?

the increase in the length from the original of the spring

If an object is elastic, how does it behave?

an object that regains its original shape when the forces deforming it are removed

the extension is directly proportional to

the force applied

If we apply too big of a force,

the line begins to curve because have exceeded the Limit Of Proportionality

Hookes law

that the extension is directly proportional to the force applied provided the limit of proportionality is not exceeded.

Hookes law equation is

f=k x e


f= force (N)


k= the spring constant of spring in (N/m)


e= extension (m)

the stiffer the spring

the greater its spring constant

when an elastic object is stretched

work is done. this is stored as elastic potential energy in the object

when the stretching force is removed

this stored energy is released

Whenever an object starts to move

a force must have been applied to it

when a force moves an object

energy is transferred and work is done

Work done is equal to

the energy transferred

work done is calculated using

w=f x d


w= work done (J)


f= force (N)


d= distance (m)



what is gravitational energy

energy stored in an object because of its position in the Earths gravitational field strength



When an object is moved vertically upwards,

it gains gravitational potential energy equal to the work done on it by the lifting force



change in gravitational potential energy is calculated using

Ep = m x g x h




Ep is change in gravitational potential energy (J)


m is the mass (kg)


g is the gravitational field strength (N/kg)


h is height (m)

Power is... and can be calculated using...

power is the rate of energy transferred


p= e


-----


t


p is power (W)


e is energy (J)


t is time (s)

All moving objects have

kinetic energy

the greater the mass of an object, the greater the speed and

the more kinetic energy it has

kinetic energy equation

Ek= 1/2 x m x v2




Ek is kinetic energy (J)


m is mass (kg)


v is speed (m/s)

Summary of elastic potential energy

if object regains shape after being stretched or squashed it is described as elastic


work is done on object to stretch or squash it, so the energy transferred to it is elastic potential energy energy.


when object returns to its original shape, this energy is released

The greater the mass of object, the greater the speed and greater its

momentum

Momentum is calculated doing

p=m x v


p= momentum in (kg m/s)


m= mass (kg)


v=velocity (m/s)

whenever an object interacts

the total momentum before is equal to the total momentum afterwards provided no external forces act on them

What is the conservation of momentum?

the total momentum before the interaction is equal to total momentum after

if one side of the momentum calculation is positive

the other side is negative

When two objects are at rest

their momentum is at zero

when a force acts upon an object that is moving or is able to move

the momentum changes

If the impact time is short

the forces acting on the object are large.


As the impact time increasing the force becomes less

When two vehicles collide

the both exert equal and opposite forces on eachother and their total momentum is unchanged

When two electrically insulating objects are rubbed together

electrons are rubbed off one material and deposited on the other

Because the electrons have an negative charge

the material that gains the electrons becomes negatively charged, so the one that loses them becomes positively charged.


This is called charging by friction

a diode

allows current through it in one direction

light emitting diode

emits light when current passes through it

a fixed resistor

limits current in circuit

variable resistor

allows the current to be varied

a fuse

designed to melt and therefore break the circuit if the current through it is greater than a certain amount

LDRs

LDRs (light-dependent resistors) are used to detect light levels, for example, in automatic security lights. Their resistance decreases as the light intensity increases:In the dark and at low light levels, the resistance of an LDR is high, and little current can flow through it.In bright light, the resistance of an LDR is low, and more current can flow through it.

thermistor

Thermistors are used as temperature sensors, for example, in fire alarms. Their resistance decreases as the temperature increases. At low temperatures, the resistance of a thermistor is high, and little current can flow through them.At high temperatures, the resistance of a thermistor is low, and more current can flow through them.

potential difference =

v= W


-----


Q




v is p.d (v)


w is work done (J)


Q is charge (C)

Resistance is the opposition

to current flow

resistance is calculated using

R= V


----


i


where r is the resistance (in ohms)


v is p.d (v)


i is current (A)

Ohms law

the current is directly proportional to the potential difference across the resistor.



Any component that obeys ohms law is called an

Ohmic conductor

on a current potential difference graph for a filament bulb

the line is a curve so current is not directly proportional to the p.d.


resistance of filament bulb increases as current increases. this is because the resistance increases as the temp increases

in a series circuit, the components are connected one after another so

if there is a break in the circuit anywhere , charge stops flowing



current is

I= V


---


R

the bigger the resistance of a component

the bigger its share of the supply p.d

in a parallel circuit

each component is connected across the supply so if there is a break in one part of circuit charge can still flow in other parts

each component is connected across the p.d supply so

p.d across all components is the same

the bigger the resistance of the component

the smaller the current through it

Frequency of the UK mains supply is

50Hz which means it changes direction 50 times each second

therefore the voltage of UK mains supply is

230 volts

the frequency of an a.c supply can be determined from an oscilloscope trace using equation

f= 1


---


t


f is frequency (Hz)


t is time taken for one cycle (s)

why is the outer cover of a three pin plug made of plastic or rubber?

because both these materials are good electrical insulators

the pins of the plug are made of brass as

brass is a good electrical conductor as it is hard and will not rust or oxidise

the brown wire is

the live wire

the blue wire in the

neutral wire

the yellow and green wire is

the earth wire

appliances with metal cases must be

earthed

appliances with plastic cases do not need to be earthed because

they are said to be double insulated

in a cable, the more current to be carried

the thicker the cable

why do appliances with metal cases need to be earthed?

because if a fault develops and the live wire touches the metal cause, the case becomes live and could give and electric shock to anyone who touches it

the rating of the fuse should be slightly higher than the normal working current of the appliance because

if it is much higher, it will not melt soon enough to break the circuit and if it is not higher than the normal current it will melt as soon as the appliance is switched on

what is a circuit breaker?

an electromagnet switch that opens and cuts off the supply if the current is bigger than a certain value

what is a RCCB? (residual current circuit breaker)

cuts of the current in the live wire if it is different to the current in the neutral wire.


it works faster than a fuse or ordinary circuit breaker

when a charge flows through an appliance, electrical energy is transferred to other forms. in a resistor

electrical energy is transferred to the resistor so the resistor becomes hotter

the nuclei of a radioactive substance is

unstable

how does the nuclei of a radioactive substance become stable?

Radioactive Decay

Name the three types of radiation emitted

alpha, beta , gamma

Background radiation is

around us all the time. it is from radioactive substances in environment, from space, and devices like x rays

Rutherford, Geiger and Marsden devised an

alpha particle scattering experiment, in which they fired alpha particles at thin gold foil

What did they discover in Rutherfords experiment

most of the alpha particles passed straight through the foil, this means that most of the atom is just empty space.


some of the alpha particles were deflected through small angles which suggests that the nucleus has a positive charge.


a few rebound through very large angles. this suggests that the nucleus has a large mass and a very large positive charge

What happens in alpha decay

the nucleus loses 2 protons and 2 neutrons

What happens in beta decay?

a neutron in the nucleus changes into a proton and an electron

an isotope is

same element with different number of neutrons in nucleus

Atomic number

number of protons in atom

Mass number

protons plus neutrons

Beta is a

high speed electron from nucleus, emitted when neutron in nucleus changes to a proton and electron.



0


Represented as B


-1

Gamma ray is

electromagnetic wave released from nucleus with no overall charge

Alpha is

made up of two protons and two neutrons




when a nucleus emits alpha particle the atomic number goes down by two and the mass number goes down by four

What is ionisation?

when nuclear radiation travels through a material it will collide with the atoms of a material and knock the electrons off creating ions

Alpha particles properties

relatively large so have lots of collisions with atoms, they are strongly ionising.


they can be stopped by thin sheet of paper human skin or few cm of air


alpha particles have positive charge so are deflected by electric and magnetic fields


Very ionising as once in body can not escape out

beta particle properties

much smaller and fast than alpha so less ionising and penetrate further


blocked by few metres of air or thin sheet of aluminium


negative charge and are deflected by electric and magnetic fields in opposite direction to alpha particles

Gamma particle properties

electromagnetic waves so will travel long way through material before colliding with atom


weakly ionising


very penetrating


stopped by several cm of lead or several metres of concrete


not deflected by magnetic or electric fields

What is the half life of a radioactive isotope?

the average time it takes for the number of nuclei of the isotope in a sample to halve

the activity of a radioactive source is

number of nuclei that decay per second

number of atoms of radioactive isotope and activity

both decrease by half every half life

Alpha sources are used in

smoke alarms

beta sources used for

thickness monitoring

gamma and beta sources used as

traces in medicine. it is swallowed or injected and its progress around the body is monitored by a detector outside the patient

radioactive dating is used for

finding the age of ancient material.


carbon dating used to find age of wood and other organic material


uranium dating used to find age of igneous rocks

nuclear fission is the

splitting of atoms nucleus

what two fissionable isotopes are commonly used in a nuclear reactor?

uranium-235 and plutonium-239


uranium 235 is most commonly used

Nuclear fission process

for fission to occur the uranium 235 or plutonium 239 nucleus must absorb a neutron.


the nucleus then splits into two smaller nuclei.


in this process two or three more neutrons are emitted and energy is released. the energy released in such a nuclear process is much greater than the energy released in a chemical process such as burning

When does a chain reaction occur?

A chain reaction occurs when each fission event causes further fission events. In a nuclear reactor the process is controlled so one fission neutron per fission on average goes on to produce further fission


this takes place in a reaction chamber/ fuel rods

What is nuclear fusion?

process of forcing two nuclei close enough together so they form one single larger nucleus

nuclear fusion happens as

they make two light nuclei collide at very high speed

fusion is the process by which energy is released in

stars

nuclei approaching eachother will repel due to their positive charge so to over come this

the nuclei must be heated at very high temperatures and reaction must be contained by a magnetic field

to reduce exposure to radiation, workers must

keep as far as possible from sources of radiation


spend as little time exposed as possible


shield themselves with materials such as concrete and lead

most scientists believe earth was created by big bang

13 billion years ago

protostars are formed by

dust and gas being pulled together by gravitational forces

the protostar becomes denser and

the nuclei of hydrogen and other light elements fuse together. energy is released from process so core gets brighter and hotter

stars radiate energy because of

hydrogen fusion in core. this stage can continue for billions of years until the star runs of out hydrogen nuclei.

a main sequence star is when

the star is stable because the inward force of gravity is balanced by the outward force of radiation from core

eventually a star runs out of hydrogen nuclei...

swells, cools down and turns red

Now, if the main sequence star has a low mass...

is now a red giant


helium and other light elements fuse to form heavier elements


fusion stops and the star will contract to form a white dwarf


eventually no more light is emitted so it becomes a black dwarf



Now if the main sequence star has a larger mass

it is a red super giant which continues to collapse


eventually the star explodes into a supernova


the outer layers are thrown out into space and the core is left as a neutron star


if this is massive enough it becomes a black hole


the gravitational field strength of the black hole is so strong that not even light can escape from it

chemical elements are formed by

fusion processes in stars

elements heavier than iron are

only formed in the final stages of the life of a big star.


this is because the process requires the input of energy

The presence of heavier elements in the sun and inner planets are

evidence that they were formed from debris scattered by supernova