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BMAT > Physics > Flashcards

Physics Flashcards

1
Q

How to charge insulators

A

Friction

Negatively charged e- are rubbed off on one material and onto the other

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2
Q

What is charging caused by

A

Gain or loss of electrons

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3
Q

When is a material negatively charged

A

Gaining e-

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4
Q

When is a material positively charged

A

Losing e-

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5
Q

Force equations

A

F= ma
F = momentum/time
F = area* pressure
Work done = force * displacement

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6
Q

Energy eqautions

A

Kinetic energy = 0.5mv^2
Gravitational Potential energy = mgdeltah
Energy transferred = VIt

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7
Q

Power equations

A 
P = work done/time
P = energy transferred / time
P = force * velocity
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8
Q

Electrical Equations

A 
Q = It
V = IR
P = IV = I^2R = V^2/R
V = E/Q
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9
Q

Electrical symbols and standard units

A 
R - resistance (ohms)
P - power (W, watts)
Q - charge (C, coulombs)
V - voltage (V, volts)
I - current (A, amperes)
E = energy, J
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10
Q

SI prefixes

A 
Giga - 10^9
Mega - 10^6
Kilo - 10^3
Hecto - 10^2
Deci - 10^-1
Centi - 10^-2
Milli - 10^-3
Micro - 10^-6
Nano - 10^-9
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11
Q

Uses of electrostatics

A

Paint sprayers
Dust Precipitators
Defribillators
Photocopiers

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12
Q

Paint sprayers as a use of electrostatic

A 
Spray can charged and charges drops
Drops repel (like charge) but attracts object to be spray painted - gives fine spray and even coat
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13
Q

Dust Precipitators as use of electrostatics

A

Cleans up emissions
Smoke particles get -vely charged by wire grid
Attracted to +vely charge plates and stick together
When heavy enough fall off or knocked off

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14
Q

Risks of static electricity

A

Charge can build up on clothing made from synthetic materials - cause spark, dangerous near inflammable gases or fuel fumes
Fuel flowing out of filler pipe, paper dragging over rollers, grain shooting out of pipes - lead to spark –> explosion

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15
Q

Role of earthing

A

Prevents dangerous sparks by providing an easy route for the static charges to travel into the ground
Charge unable to build up

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16
Q

Earthing

A

Connecting a charged object to the ground using a conductor e.g copper wire

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17
Q

Current

A

Rate of flow of e- around circuit
Flows from +ve to -ve
Only flows through component if there’s a voltage across it

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18
Q

Voltage

A

Driving force that pushes current around
Energy that each charged particle transfers passing through a component
Higher voltage, more current

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19
Q

Resistance

A

Slows down flow of e- (-ve to +ve)

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20
Q

Circuit diagrams

A

Ammeter, component and resistors placed in series - any order
Voltmeter parallel to component under test

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21
Q

AC vs DC

A

AC - constantly changing direction, AC of 5Hz = changes direction 5 times (mains supply), gives regularly repeating wave on oscilloscope
DC - current flowing in only direction (cells and batteries), straight line on oscilloscope due to same voltage

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22
Q

Calculating frequency of AC supply (Hz)

A

1/time period

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23
Q

Diode

A

Device made from semi conductor material e.g. silicon
Lets current flow freely through it only one direction (high resistance in reverse)
Can convert ac to dc

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24
Q

V-I graph for fixed resistor

A

y=x

Proportional

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25
Q

V-I graph for filament lamp

A

S shape

As filament temp increases, the resistance increases

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26
Q

NTC thermistors

A

Temp dependent resistors
As temp increases, resistance decreases
Useful temp detectors

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27
Q

LDR

A

Light dependent resistors
Resistance falls with increase in LI
Useful in automatic night lights

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28
Q

Series circuits

A

Components connected line to line, end to end
Total pd of cells shared by diff components
Current flows from +ve to -ve and is the same everywhere
Total resistance is sum of all resistances

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29
Q

Parallel circuits

A

Each component is separately connected, removal or disconnection wont affect others
Pd is same across all components
Current shared by diff components
Total resistance is ALWAYS less than branch w/ lowest resistance

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30
Q

Magnetic field

A

Region where magnets, magnetic materials and wires carrying current experience a force
Field lines go from North to South
Stronger the field, closer field lines

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31
Q

Where’s the magnetic field strongest

A

North and south poles

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32
Q

Induced magnets

A

Magnetic materials that turn into magnets when they’re in a magnetic field
Loses magnetism when magnetic field is taken away
Magnetic field encourages electrons to align, forming north and south pole

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33
Q

Which materials can become induced magnets

A

Nickel
Iron
Steel
Cobalt

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34
Q

Soft magnetic material

A

Quick and easy to magnetise and demagnetise. Lose magnetic properties quickly when left field e.g iron

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35
Q

Hard magnetic material

A

Harder to magnetise
Retain magnetic properties for way longer/permanently
V diff to demagnetise e.g. steel

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36
Q

Creating a magnetic field

A

When current is flowing through a wire a magnetic field is created
Made up of concentric circles perpendicular to wire
Right hand thumb rule can show the direction of the field
Strength of field increases w/ vicinity to wire and increases w/ current

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37
Q

Solenoid

A

Coil of wire

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38
Q

Magnetic field of solenoid

A

Outside - same as bar magnet

Inside - strong and uniform

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39
Q

Increasing magnetic field strength around electromagnet

A

Increasing current
More turns on solenoid
Adding core of soft iron inside the solenoid - iron becomes induced magnet and magnetic fields combine

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40
Q

How does current flow

A

Positive to negative

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41
Q

Motor effect

A

When a current-carrying wire in a magnetic field experiences a force

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42
Q

Factors affecting size of force due to motor effect

A

Size of current (+ve)
Magnetic flux density (shows strength of magnetic field +ve)
Length of conductor inside the field (+ve)

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43
Q

When will a wire feel the full force

A

At a right angle to the magnetic field

Experiences some force at other angle but none parallel

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44
Q

Calculating size of the force acting on conductor created by motor effect

A

When current is at 90 degrees use F=BIl

B - magnetic flux density (tesla -T)
I - current (A)
l - length (m)

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45
Q

Fleming’s left-hand rule

A

First finger pointing in direction of field
Second finger pointing in direction of current
Point out thumb so it 90 degrees to both fingers - motion

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46
Q

Fleming’s right hand rule

A

Use thumb to point in direction of current and fingers will tell you directon of field

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47
Q

Construction of dc motor (dynamo)

A

Loop of wire current flowing in opp directions on either side placed in a magnetic field
Creates moments on both lhs and rhs and the loop rotates, split ring commutator allows it to keep rotating past 90 degress (reverses direction of current) - generates direct current

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48
Q

Factors affecting magnitude of force in dc motors

A

Size of current
Strength of magnetic field
Put more turns on the coil

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49
Q

Applications of electromagnets

A

Loudspeakers
Bell
Relay

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50
Q

When is a voltage induced in a conductor (electromagnetic induction)

A

When a magnetic field changes or a wire cuts magnetic field lines

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51
Q

When can cause a magnetic field to change

A

The conductor is moving into, or out of, a magnetic field
A magnet is moving towards, or away from, the conductor
The magnetic field is being varied

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52
Q

Factors affecting magnitude of induced voltage

A

Using a stronger magnet (+ve)
Rate of change of strength of mf (+ve)
Increasing no. turns (+ve)
Speed of movement (+ve)

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53
Q

Factors affecting direction of induced voltage

A

Direction of movement

Reversed when direction of cutting mf lines reverses, increasing mf in a coil change to one decreasing (and vice-versa)

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54
Q

What can induced voltage produce

A

Induced current if the conductor is connected in a complete circuit
This current will prodce a magnetic field that opposes the change that whch induced the current

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55
Q

Conductor

A

Material which allows an electrical current to pass through it easily. It has a low resistance

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56
Q

Ac generator

A

Device producing a potential diff

Consists of a coil of wire rotating in a magnetic field

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57
Q

Operation of ac generator

A

Coil is rotated in the magnetic field inducing a current in the coil which flows into an external circuit
Requires 2 split rings
As one side of the coil moves up through the mf, pd is induced in one direction, this reverses when rotation continues and the coil moves down
Creating ac

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58
Q

Factors affecting maximum output voltage (+current)

A

Rate of rotation (+ve)
Strength of mf (+ve)
Coil has greater area (+ve)
No. turn on the coil (+ve)

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59
Q

Graphical rep of output voltage of ac generator

A

Sine graph w/ induced potential diff on y and time on x

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60
Q

Why is there no induced voltage when the coil is at 0 and 180 degrees

A

Coil is moving parallel to the direction of the magnetic field

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61
Q

Applications of electromagnetic induction

A

Car engines use an alternator to keep the battery charged and an electrical system while engine works
Hydroelectric dams

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62
Q

Step up transformer

A

Increases voltage of ac
Higher pd and more turns on 2’ coil
Useful as decreases current and resistance so less energy is lost by heating - power lines

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63
Q

Step down transformer

A

Decreases voltage of ac
Higher pd and more turns on 1’ coil
Reduces pd of supply before reaching hmes

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64
Q

Components of a transformer

A

Ac input leading to primary coil
Iron core w/ mf
Secondary coil leading to ac output
Uses generator effect

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65
Q

Transformer eqns

A

Vp/Vs = np/ns
V - potential diff
n - no. turns

VsIs = VpIp (power output at 2’ = power input at 1’)
I - current

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66
Q

Consequence of 100% efficiency

A

Total transfer of electrical power

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67
Q

Need for high voltage in electrical power transmission

A

Higher voltage, lower current –> lower resistance losses –> lower energy losses

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68
Q

Types of forces

A 
Weight 
Normal contact
Drag (air resistance)
Friction
Magnetic
Electrostatic
Thrust
Upthrust
Lift 
Tension
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69
Q

Hooke’s law

A

F = ke

F - force (N)
k - spring constant (N/m)
e - extension (m)

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70
Q

Spring constant

A

Measure of the stiffness of a spring up to its limit of proportionality or elastic limit
Higher k, stiffer spring

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71
Q

Limit of proportionality

A

Point beyond which Hooke’s law is no longer true when stretching a material

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72
Q

Elastic limit

A

Furthest point a material can be stretched/deformed while being able to return to its previous shape, becomes inelastic after

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73
Q

Force extension graphs

A

Directly proportional until limit of proportionality - rate slows down (non-linear extension and inelastic deformation)

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74
Q

What happens when a spring is extended/ compressed

A

Work is done

Provided there’s no inelastic deformation work done = elastic potential stored

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75
Q

Elastic potential energy

A

E = 1/2 k x^2

E - energy (J)
k - spring constant (N/m)
e - extension/compression (m)

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76
Q

Mass

A

Property that resists change in motion (inertia)

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77
Q

What happens at terminal velocity

A

Object moves at a steady speed in constant direction because the resultant force acting on its 0

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78
Q

Stages of falling through a fluid

A

Object accelerates downwards (gravity)
As speed increases as does frictional forces
At terminal velocity weight is balanced by frictional forces

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79
Q

Inertia

A

Tendency of an object to continue in its current state (at rest or in uniform motion)

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80
Q

Newton’s 1st Law

A

Object remains in same state of motion unless a resultant force acts on it

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81
Q

Examples of Newton’s 1st law

A

Runner experiences same air resistance as thrust

Object at terminal velocity experiences same air resistance as weight

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82
Q

Newton’s Second Law

A

Resultant force = m x a

a is proportional to resultant force and inversely proportional to mass

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83
Q

Inertial mass

A

Ratio of force over acceleration

Measure of how diff it is to change velocity

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84
Q

Factors affecting air resistance

A

Speed
Surface area (+ve)
Air flow - turbulent (+ve) vs streamlined

85
Q

Equation for momentum

A

mass * velocity

Force is the rate of change of momentum (kgm/s)

86
Q

Equation for work done

A

Force * distance

87
Q

What happens hen force moves an object

A

Energy is transferred and work is done

88
Q

Calculating % efficiency

A

Useful output/ total input * 100

89
Q

Factors affecting rate of conduction

A 
Temp diff 
Cross-sectional area
Length (distance heat must travel)
Substance between 2 objects (better/worse thermal conductor)
Time
90
Q

Heat vs temp

A

Temp is a measure of how hot something is - degrees
Heat is a form of energy - joules
Flows between things of diff temps

91
Q

Transfer of heat

A

Conduction
Convection
Radiation

92
Q

Good conductors

A

Metal

93
Q

Poor conductors

A

Insulators - non metals and gases

94
Q

Fluids

A

Anything that can be made to flow

95
Q

When does convection occur

A

When particles w/ a lot of heat energy in a liquid or gas move and take the place of those w/ less heat energy

96
Q

Why does convection occur

A

Liquids and gases expand when heated (higher kinetic energy) –> take up more vol
Also less dense so rises

97
Q

What allows convection currents to work

A

Diff in differences of density of heated particles and cooler ones

98
Q

Thermal radiation

A

Electromagnetic waves in the infrared region

Requires waves not particles - works through a vacuum

99
Q

Radiation properties of dull, matt or rough surfaces

A

Good absorption and emission

100
Q

Radiation properties of shiny surfaces

A

Poor absorption and emission

Good reflectors

101
Q

Factors affecting radiation

A

Type of surface

Size - thin and flat > fat

102
Q

Eqn for spp heat capacity

A

thermal energy / (mass * deltat)

103
Q

Internal energy of a system

A

Total energy that its particles have in their kinetic and potential energy stores

104
Q

What happens when a system is heated

A

Transfers energy to its particles (gain kinetic energy), increase in internal energy
Leads to change in temp or state

105
Q

What does size of temp change depend on

A

Mass of substance
Spp heat capacity
Energy input

106
Q

Latent heat

A

Energy needed to change state of a substance

107
Q

Spp latent heat

A

Energy needed to change 1kg of a substance from one state to another w/out changing it’s temp

108
Q

Spp latent heat of fusion

A

Spp latent heat for changing between a solid and liquid

109
Q

Spp latent heat of vaporisation

A

Spp latent heat for changing from liquid –> gas

110
Q

Spp latent heat eqn

A

E = mL

E - energy for change in state (j)
m - mass (kg)
L - spp latent heat (j/kg)

111
Q

Gas temp

A

Increase in temp –> transfer of energy into the ke stores of the particles
Higher temp, higher avg energy (higher avg speed)

112
Q

Outward gas pressure

A

Total force exerted by all particles in the gas on a unit area of the container walls

113
Q

Increasing gas pressure

A

Incresed temp –> more ke –> more collisons

Decreased vol

114
Q

Relationship between pressure and vol of gases

A

PV = constant

P - pressure
V - vol

Inversely proportional - valid for a gas of fixed mass at a constant temp

115
Q

Density

A

Measure of how close together the particles in a substance are

Mass/vol

116
Q

How does depth affect pressure of liquids

A

As depth increases as does no. particles above that point

Weight adds to pressure experienced at that point

117
Q

Eqn for hydrostatic pressure

A

p = h rho g

p - pressure (Pa)
h - depth (m)
rho - density (kg/m^3)
g - gravitational field strength (N/kg)

118
Q

Measuring density of irregular solid

A

Measure mass w/ balance
Fill eureka can (displacement can) just below spout and place solid inside can
Collect water that pours out and that is the solids vol and you can use rho=m/v

119
Q

Measuring density of liquid

A

Place measuring cylinder on balance and zero it
Add 10 ml and record total vol and mass
Repeat until cylinder is full
Calculate density for each measurement and find avg

120
Q

Representation of waves

A

Displacement on y and distance on x axis

Crests/peaks and troughs show maximum +ve and -ve displacement fom rest

121
Q

Amplitude

A

Heigh of peak

Max displacement from eqm

122
Q

Wavelength

A

Peak to peak or trough to trough

123
Q

Frequency

A

No. complete waves passing in one second
1 Hz = 1 wave per second
1/period

124
Q

Waves

A

Vibrations transferring energy by causing particles (or fields) to vibrate

125
Q

Types of wave

A

Transverse e.g water ripples, EM waves, seismic S waves

Longitudinal e.g sound, seismic P and ultrasound waves

126
Q

Longitudinal waves

A

Vibrations are parallel to direction of wave travel

Show areas of compression and rarefaction

127
Q

Compressions

A

Regions of high pressure due to particles being close together
Occurs when particles in the medium are pushed closer as the wave passes
Particles move backwards and forwards between compressions

128
Q

Rarefactions

A

Regions of low pressure due to particles being spread further apart
Occurs when particles in the medium are pulled further apart as the wave passes

129
Q

Transverse waves

A

Vibrations are at right angles to direction of wave travel
Energy is transferred from left to right
Particles move up and down as the wave is transmitted through the medium

130
Q

Wave period

A

Time taken to complete one cycle

Inversely proportional to frequency

131
Q

Calculating wave speed

A

Distance/ time OR

Frequency * wavelength

132
Q

When does reflection occur

A

At a surface

133
Q

Refraction

A

Change in direction of a wave at a boundary of 2 transparent materials
Can cause optical illusions as the light waves appear to come from a diff position to actual source

134
Q

When does light bend towards the normal

A

When light goes from a less dense medium to a more dense medium

135
Q

When does light bend away from the normal

A

When light goes from a more dense medium to a less dense medium

136
Q

Effects of refraction

A

Freuency remains the same

If waves slows, wave length decreases (proportional)

137
Q

Effects of reflection

A

Wavelength, freq and speed stay the same

138
Q

Doppler effect

A

Observed frequency of source is less or more than the true frequency
Faster observer approaches or recedes from the source, the greater the shift in freq. and wavelength

139
Q

Production of sound waves

A

Vibrating source - these vibrations can travel through solids, liquids and gases
Speed travels 330m/s in air
Cannot travel in a vacuum - no particles to carry vibrations

140
Q

Frequency of sound waves

A

High freq = high pitch

Low freq = low pitch

141
Q

Amplitude of a sound wave

A

High amp = loud (more energy)

Low amp = quiet

142
Q

Range of human hearing

A

20 Hz to 20kHz

Range of frequencies that’ll cause the ear drum to vibrate

143
Q

Echoes

A

Reflection of sound waves at a surface

144
Q

Ultrasound waves

A

Have a frequency higher than 20,000 H

145
Q

Partial reflection

A

When ultrasound meets a boundary between substances some is reflected and some transmitted (and possible refracted)

146
Q

Uses of ultrasound

A

Med - Prenatal scanning, breaking kidney stones
Industry - finding fault in materials and echo scanning
Cleaning jewellery - vibrations caused by waves shake apart dirt

147
Q

How ultrasound scanning works

A

Time between emission of waves and detection of partially reflected ultrasound waves can be interpreted and used to determine locations of boundaries and form images of structures hidden from view

148
Q

Echo sounding

A

Sonar used by boats and submarines, where sound waves help identify depth of water or location of objects in deep water

149
Q

Properties of electromagnetic waves

A

Transverse waves

Travel at the speed of light

150
Q

Components of EM spectrum

A

From lowest to highest energy and freq and longest to shortest wavelength

Radio waves
Microwaves
IR
Visible light 
UV
X-rays
Gamma
151
Q

Uses of radio waves

A

TV signals - long wavelength means they travel further in Earth’s atmosphere

152
Q

Uses of microwaves

A

Cooking - waves absorbed by water molecules casing vibrations (heat)
Mobile phones - wavelength penetrates our atmosphere

153
Q

Uses of IR

A

Optical fibre communication (TV remotes)

154
Q

Uses of visible light

A

Seeing - only part of spectrum we can see

155
Q

Uses of X-rays

A

Medical images of bones - absorption produces an image

156
Q

Uses of gamma radiation

A

Killing cancer cells - highly penetrative

Sterilising food

157
Q

Which parts of the EM spectrum can be harmful

A 
The higher the frequency of the radiation, more likely its going to cause damage 
Microwaves
IR
UV
X-rays
Gamma
158
Q

Hazards of microwaves

A

Internal heating of body tissues

159
Q

Hazards of IR

A

Can cause skin to burn as is felt as heat

160
Q

Hazards of X -rays and gamma rays

A

Damage cells causing mutations (cancer) and cell death

161
Q

EM spectrum

A

Continuous spectrum of all the possible wavelengths of EM waves

162
Q

Uses of UV

A

Energy efficient lamps and sun tanning lamps

163
Q

Hazards of UV

A

Premature skin aging
Increased risk of skin cancer
Cataracts

164
Q

Radiation dose

A

Measure of the risk of harm due to exposure to radiation
Measure of Sieverts
1000mSv = 1 Sv

165
Q

Nuclide

A

More generic term for isotope
Used when referring to nuclei of DIFF elements and isotopes are used when referring to sev. diff nuclides of the SAME element

166
Q

What does an unstable nucleus cause

A

Emissions. These are random

167
Q

Types of emission

A

Alpha
Beta
Gamma

168
Q

Alpha particles

A

4 He 2 nuclei so atomic no . 2 and atomic no. 4
Relatively big and heavy and slow moving (0.1c)
Strongly ionising
Don’t penetrate far and stopped v quickly
Deflected by magnetic and electric fields (attracted to -ve)

169
Q

Beta particles

A

e- so increases atomic no. +1
V small and move quickly (0.8c)
Penetrate moderately before colliding
Moderately ionising
For every beta particle emitted a neutron converts to a proton
Deflected by magnetic fields and electric fields (attracted to +ve)

170
Q

Gamma radiation

A 
Photon w/ no mass and no charge 
V quick (c)
Penetrate long way into materials 
Weakly ionising - tend to pass through atoms
After an alpha or beta emission, nucleus sometimes has extra energy to get rid of so emits a gamma ray
171
Q

Sources of background radiation

A 
Radon gas
Cosmic rays 
Medical X - rays 
Rocks and building materials 
Food
172
Q

When do alpha and beta particles experience a deflecting force

A

When they move in magnetic fields - provided their motion isn’t parallel to the field
beta deflects more - lower mass, lower charge

173
Q

Uses of ionising radiation

A

Smoke detectors - alpha
Tracers in med - short half-life gamma emitters
Radiotherapy - gamma rays
Sterilisation of food and surgical instruments - gamma rays

174
Q

Radiotherapy

A

Used in conjunction w/ chemo to kill cancerous cells

High dosage of gamma rays directed carefully to treat cancers

175
Q

Smoke detectors

A

Weak source of alpha radiation placed in detector, close to 2 electrodes
Causes ionisation and a current flows
Smoke absorbs radiation, current stops –> alarm sounds

176
Q

Tracers in med

A

Iodine-131 is absorbed by thyroid and gamma rays can detect and indicate whether thyroid is working correctly
Only gamma and beta emitters w/ short half lives can be taken into the body - so radiation can pass out of the body

177
Q

Sterilisation

A

High dose of gamma rays will kill all microbes

Irradiation allows food and plastic items to be sterilised w/ out boiling

178
Q

If the radioactive source is inside the body …

A

alpha is most dangerous - easily absorbed by cells

beta and gamma less likely to be absorbed and will usually pass through it

179
Q

If the radioactive source is outside the body ..

A

beta and gamma are most dangerous - penetrate skin and damage cells inside
alpha unlikely to react to living cells inside the body

180
Q

Charging by induction

A

Neutral object placed near a charged object can become charged

181
Q

Types of charging by induction

A

Magnetic - unmagnetized iron next to magnet

Electrostatic

182
Q

Sparking

A

Occurs when the air between 2 objects becomes ionised by a large voltage and therefore starts conducting

183
Q

Milliamp

A

1 * 10^-3

184
Q

Microamp

A

1 * 10^-6

185
Q

Kilohm

A

1 * 10^3

186
Q

Megohm

A

1 * 10^6

187
Q

Identifying poles on solenoids

A

If the current is circulating clockwise - south pole

Anti-clockwise - north pole

188
Q

Electromagnet vs permanent magnet

A

E - can be switched on/off, vary strength of mf, can reverse polarity, made from soft magnetic material
Permanent - opposite

189
Q

Electromagnet

A

Many turns of insulated wire wound onto soft iron

Current creates external magnetic field

190
Q

Typical voltage output of a power station

A

11 kV or 33 kV

191
Q

Transmission voltage in UK

A

275 kV or 400kV

192
Q

SUVAT eqns

A

v = u +at
s = 1/2 (u+v)t
v^2 - u^2 = 2as

193
Q

g on the Moon

A

1.6 N kg-1

194
Q

g on Jupiter

A

26 N kg-1

195
Q

g on the Sun

A

280 N kg-1

196
Q

Convection vs conduction

A

Conduction - Can occur in solids, heat is transferred by microscopic motions of individual particles

Convection - Cannot occur in solids, heat is transferred by macroscopic motion of large no. particles

197
Q

Converting density

A

1 g cm-3 = 10^3 kg m ^-3

1 kg m-3 = 10-3 g cm -3

198
Q

Mechanical waves

A 
Sound 
Ultrasound
Seismic waves 
Water waves 
Waves on a string 
Wavs on a slinky
199
Q

Incident energy =

A

Reflected energy + transmitted energy + absorbed energy

200
Q

Source and observer approaching one another

A

Shorter wavelength

Higher freq

201
Q

Source and observer moving away from one another

A

Longer wavelength

Lower freq

202
Q

Using reflection to measure distances

A

d = vt/2

t - time for pulse to travel and return
v - speed of sound in medium

203
Q

Absorption of EM waves

A

EM waves transfer energy from source to absorber
When absorbed, energy transferred to matter that absorbs them
Can cause heating, e- at surface to vibrate at freq. of waves, ionisation

204
Q

Red light

A

Long wavelength

Low freq

205
Q

Violet light

A

Short wavelength

High freq

206
Q

c

A

Speed of light

3 * 10 ^8 m/s

207
Q

Penetrating ability of alpha

A

Blocked sheet of paper and human skin

Penetrate few cm in air

208
Q

Penetrating ability of beta

A

Typically blocked by thin metal
Not blocked by human skin
Penetrate up to sev. m in air

209
Q

Penetrating ability of gamma rays

A

To block it to large extent requires sev cm of very dense material e.g. lead
Can penetrate up to hundreds of m in air

BMAT (3 decks)

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