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last minute cram Flashcards

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1
Q

what is centre gravity/mass

A

the point where all the mass can considered to be concentrated

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2
Q

Describe an experiment to determine the
position of the centre of gravity of an irregularly
shaped plane lamina

A

make 2 holes in lamina near the edge. draw 2 straight lines from hole and intersection is centre of gravity.forces must be balanced for it to be in equilibrium

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3
Q

state hookes law

A

extension is directly proportional to load (if elastic limit is not yet exeeded

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4
Q

formula for resultant force (change in momentum perunit time

A

∆p/∆t

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5
Q

electromagnetic spectrum in order of frequency

A

radio, wicro, infrared, visible light, ultra violet, x rays, gamma rays

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6
Q

what is monochromatic light

A

visible light of a single frequency

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7
Q

what are radio waves used for

A

radio, television transmissions, astronomy, RFID

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8
Q

what are microwaves used for

A

satellite tv, mobile phones, microwave ovens

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9
Q

define waves

A

the transfer of energy without transferring matter

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10
Q

what is newtons first law

A

when all forces acting upon an object are balanced (equal), means the object will remain stationary or travel at terminal velocity. no resultant force

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11
Q

what is newtons second law

A

when all forces acting on an object are unbalanced; meaning there is a net/resultant force which causes the object to accelerate

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12
Q

what is newtons third law of motion

A

for every action, there is an opposing reaction (opposite reaction)

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13
Q

is velocity constant in circular motion?

A

no

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14
Q

7 types of stored energy

A
  • chemical potential
  • hydro
  • geothermal
  • nuclear
  • heat
    -light
  • wind
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15
Q

what is boyles law

A

relationship of pressure and volume (mass and temp stay constant). pressure is inversely proportional to volume

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16
Q

formula for boyles law

A

P1 x V1 = P2 x V2

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17
Q

what is charles law

A

the volume of a fixed amount (constant mass) of a gas is directly proportional to the temperature of the gas when the pressure is held constant

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18
Q

what is the formula for charles law

A

v= TK
volume = temp x constant

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19
Q

What is pressure law

A

pressure of a fixed amount is directly proportional to the temperature of a gas (volume is constant)

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20
Q

what is the formula of pressure law

A

P1/T1 = P2/T2

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21
Q

what is the ideal gas formula

A

PV = nRT
pressure x volume = moles x constant x temperature

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22
Q

factors affecting evaporation

A
  • humidity
  • wind speed
  • temperature
  • surface area
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23
Q

are melting , evaporation and boiling endothermic?

A

yes

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24
Q

what is conduction

A

main method of conduting heat in solids. occurs when heat source close to an object causes an increase in kinetic energy of particles, leading to faster particles collide with slower vibrating ions in the lattice of solid, transfering energy until thermal equilibrium is reached

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25
Q

2 features of insulators

A
  • no free moving electrons
  • ‘slower’ and larger particles
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26
Q

what is convection

A

flow of heat through a fluid from rising of less dense higher temperature fluid, then cooling and sinking, creating a convection current

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27
Q

what is radiation

A

flow of heat from one place to another without particle contact (electromagnetic waves)

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28
Q

what does an object need to do to be at constant temperature?

A

transfer energy away at the same rate it receives energy (thermal equilibrium)

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29
Q

good emitters

A
  • black surfaces
  • dull
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30
Q

good relectors

A
  • white
  • shiny
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31
Q

good absorber

A

black

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32
Q

poor absorber

A

white

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33
Q

what is the wavelength

A

distance between 2 conservative corresponding points

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34
Q

what is amplitude

A

the distance between the undisturbed (middle) of the wave to the crest/trough (lambda)

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35
Q

what is frequency

A

number of waves passing through a point in one second (hertz)

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36
Q

define transverse wave

A

vibrations of the particles are perpendicular to the direction of the wave

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37
Q

4 examples of transverse waves

A

water waves, light, electromagnetic waves,, seismic S waves

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38
Q

define longitudinal waves

A

vibrations of the particles are parallel to the direction of the wave (cant travel through a vacuum)

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39
Q

give 3 examples of longitudinal waves

A

sound waves, seismic P waves, pressure waves

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40
Q

what are 2 regions of longitudinal waves called

A

compression (tight) and rarefraction (spread out)

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41
Q

what do waves transfer

A

energy, information

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42
Q

what is reflection

A

occurs when a wave hits a boundary between two media and does not pass through, but stays in the original medium

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43
Q

what is the law of relection

A

angle of incidence = angle of reflection

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44
Q

define refraction

A

when a wave enters a different medium, the speed can change. this effect is called refraction and occurs when a wave passes a boundary between two different media, undergoing a change in speed

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45
Q

what happens during refraction

A
  • change in wavelength (frequency stays the same)
  • change in direction
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46
Q

what happens when waves slow down?

A

waves will turn slightly towards the normal (cause them to bunch up and wave length decreases)

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47
Q

what happens when waves speed up?

A

waves will turn slightly away from the normal (causes waves to spread out, causing wave length to increase)

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48
Q

what is diffraction

A

when waves pass through a narrow gap, they spread out

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49
Q

what happens to wavelength during diffration

A

remains constant

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50
Q

factors that affect diffraction

A
  • smaller gap (greater diffraction(
  • larger wavelength
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51
Q

when is diffraction most prominent

A

when width of the gap compared to wavelength are approximately equal

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52
Q

what is the refractive index

A

number related to speed of light in a material

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53
Q

what is refractive index formula

A

speed of light in a vacuum/speed of light in a material (always will be larger than 1)

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54
Q

what is snells law

A

when light enters a denser medium, it slows down and bends towards the normal

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55
Q

what is snells formula

A

n = sin(i)/sin(r)
refractive index = sin(angle of incidence)/sin(angle of refraction)

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56
Q

critical angle formula

A

1/sin(c)
1/sin (crictical angle)

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57
Q

which 3 elements are magnetic

A
  • iron
  • copper
  • cobalt
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58
Q

difference between hard and soft iron

A

hard = maintains magnetism for a long time
soft = magnetized quickly, but gets demagnetized quickly when external magnetic field is removed

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59
Q

what is a magnetic field

A

the region around a magnet where a force acts on another magnet/magnetic material

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60
Q

what is an electrical field

A

region where charges experience force

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61
Q

which way are electric field lines pointing?

A

away from positive charges (toward negative charges)

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62
Q

what are field lines in an electric field described as?

A

the direction of the force on a positive charge at that point

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63
Q

what factor does electric fields rely on?

A

distance from the object (field is strongest closest)

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64
Q

what kind of force do objects in an electric field experience?

A

electrostatic force (force is vector, direction of this force depends on whether the charges are the same or opposite)

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65
Q

what is a conductor

A

material that allows charge (usually electrons) to flow through it easily

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66
Q

define current

A

rate of flow of charged particles

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67
Q

what makes conductors (metal) so good at conduction?

A
  • sea of electrons carry charge through the material
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68
Q

what is an insulator

A

material that has no free charges, hence does not allow the flow of charge through them very easily

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69
Q

4 examples of insulators

A
  • rubber
  • plastic
  • glass
  • wood
70
Q

if a non metal allows a charge to pass through, what happens?

A

not very good at conducting, however they allow a little in the form of static electricity

71
Q

what happens when GLE falls?

A

material being tested is being a good conductor

72
Q

what happens when GLE remains in place

A

material being tested is a poor conductor

73
Q

what happens when GLE falls slowly

A

material being tested is a poor conductor

74
Q

what is current

A

amount of charge passing a point in a circuit every second (charge per second)

75
Q

what is direct current

A

electrons flow in one direction only, from negative to positive terminal

76
Q

what is alternating current(AC)

A

direction of electron flow changes direction regularly

77
Q

what is conventional current

A

positive terminal to negative

78
Q

FINSIH MAGNETISM AND OTHERS

A
79
Q

what is acceleration

A

rate of change of speed

80
Q

what happens when water waves enter a shallow region

A

velocity and wave length decrease (frequency stays the same) direction will bend towards normal

81
Q

what happens when water waves enter a deep region

A

velocity and wavelength increases (frequency remains the same) direction will bend away from normal

82
Q

what is the conservation of energy

A

energy cannot be created or destroyed. energy can be transferred / transformed (between energy stores)

83
Q

what is kWh

A

energy transferred in one hour at a rate of transfer of 1 kW

84
Q

how many kilowatt kW in megawatt MW

A

1000

85
Q

how many watts W in kilowatt kW

A

1000

86
Q

what is a compression

A

region where particles are closer than normal

87
Q

what is a rarefraction

A

region where particles are further apart than normal

88
Q

what do longditudinal waves need to pass

A

need to pass through medium

89
Q

can transverse waves pass through vacuum

A

yes

90
Q

what is formula for emf

A

W/Q

91
Q

what is e.m.f

A

electrical work done by a source that moves a unit charge through the whole circuit

92
Q

why do mobile phones/wireless internet use microwaves

A

microwaves
can penetrate some walls and only require a
short aerial for transmission and reception

93
Q

what do some satellite phones use

A

low orbit artificial satellites and geostationary

94
Q

what does direct broadcast satellite television use

A

geostationary satellites

95
Q

what is infrared waves used for

A

electric grills, short range
communications such as remote controllers
for televisions, intruder alarms, thermal
imaging, optical fibres

96
Q

what is visible light waves do

A

; vision, photography, illumination

97
Q

what does uv rays do

A

security marking, detecting fake
bank notes, sterilising water

98
Q

what do x rays do

A

medical scanning, security scanners

99
Q

what do gamma ray do

A

sterilising food and medical
equipment, detection of cancer and its
treatment

100
Q

harmful exposure of microwaves lead to

A

internal heating of body cells

101
Q

harmful exposure infrared

A

skin burns

102
Q

harmful exposure uv

A

damage to surface cells and eyes, leading to skin cancer and eye conditions

103
Q

harmful exposure to x ray and gamma ray

A

mutation or damage to cells in the body

104
Q

what does bluetooth use

A

low energy radio waves or
microwaves because they can pass through
walls but the signal is weakened on doing so

105
Q

what does optical fiber use

A

(visible light or infrared) are
used for cable television and high-speed
broadband because glass is transparent to
visible light and some infrared; visible light
and short wavelength infrared can carry high
rates of data

106
Q

what is analogue signal

A

signals vary consistently (any value)

107
Q

what is digital signal

A

can only take one of 2 states

108
Q

can sound be transmitted as digital or analogue signal

A

both

109
Q

what is the benefits of digital signaling

A

increased rate of transmission of data
and increased range due to accurate signal
regeneratio

110
Q

describe production of sound

A

vibrating sources

111
Q

what is echo

A

relection of sound waves

112
Q

whats ultrasound

A

sound with frequency higher than 20kHz

113
Q

uses of ultrasound

A

nondestructive testing of materials, medical scanning
of soft tissue and sonar including calculation of
depth or distance from time and wave speed

114
Q

what is a magnetic field

A

a region in which a magnetic pole experiences a force

115
Q

what way do field lines go on a magnet

A

north to south

116
Q

hazards of electrical safety

A
  • damaged insulation
  • overheating cables
  • damp conditions
  • excess current from overloading of plugs, leads, single and multiple sockets
117
Q

what does a mains circuit consist of

A

live wire, neutral wire, earth wire

118
Q

what does a fuse do

A

protects the circuit and cabling for a double insulated appliance

119
Q

4 things in background radiation

A
  • radon gas
    -rocks/building
  • food/drink
  • cosmic rays
120
Q

what is radioactive decay

A

change in an unstable nucleus tha can result in emission of alpha, beta or gamma radiation. these are spontaneuous and random

121
Q

what is half life

A

e time taken for half the nuclei of that
isotope in any sample to decay

122
Q

what pathway shape do planets take

A

elliptical

123
Q

how long does it take for moon to orbit earth

A

one month

124
Q

what does the solar system contain

A
  • one star (sun)
  • mercury, venus, earth, mars, jupiter, saturn, uranus, neptune
  • pluto (dwarf planets) and asteroids
  • moons (orbit planet
  • smaller bodies (comets and natural satellites)
125
Q

is the sun at the centre of elliptical orbit?

A

no except when orbit is approximately circular

126
Q

what feature are the 4 planets closest to sun

A

rocky and small

127
Q

what are the 4 planets furtheret from sun features

A

gaseous and large

128
Q

why do the features of the planet link to dependence of gravity, elements in interstellar clouds of gas and dust, rotation of material in the cloud and formation of an accretion disc

A

?

129
Q

describe sun

A

star of medium size, mostly consists of hydrogen and helium, radiates most energy in infrared, visible and uv regions of electromagnetic spectrum

130
Q

what are stars powered by

A

nuclear reactions that release energy and that in stable stars the nuclear reactions involve the fusion of hydrogen into helium

131
Q

what are galaxies made of

A

billions of stars

132
Q

what is light year

A

astronomical distance measured by the distance travelled in the vacuum of space by light in one year

133
Q

one light year is equal to?

A

9.5 x 10^15 m

134
Q

life cycle of star

A

(a) a star is formed from interstellar clouds of
gas and dust that contain hydrogen
(b) a protostar is an interstellar cloud collapsing
and increasing in temperature as a result of
its internal gravitational attraction
(c) a protostar becomes a stable star when the
inward force of gravitational attraction is
balanced by an outward force due to the high
temperature in the centre of the star
(d) all stars eventually run out of hydrogen as
fuel for the nuclear reaction
(e) most stars expand to form red giants and
more massive stars expand to form red
supergiants when most of the hydrogen in
the centre of the star has been converted to
helium
(f) a red giant from a less massive star forms a
planetary nebula with a white dwarf star at
its centre
(g) a red supergiant explodes as a supernova,
forming a nebula containing hydrogen and
new heavier elements, leaving behind a
neutron star or a black hole at its centre
(h) the nebula from a supernova may form new
stars with orbiting planets

135
Q

what is approximate diameter of milky way

A

100 000 light years

136
Q

what is redshift

A

an increase in observed wavelength of electromagnetic readiation emitted from receding stars and galaxies

137
Q

is light emitted from distant galaxies redshifted in comparison with earth?

A

yes

138
Q

redshift is evidence of what

A

universe is expanding, supports big bang theory

139
Q

what is microwave radiation

A

f a specific
frequency is observed at all points in space
around us and is known as cosmic microwave
background radiation (CMBR

140
Q

when was CMBR produced

A

shortly
after the Universe was formed and that this
radiation has been expanded into the microwave
region of the electromagnetic spectrum as the
Universe expanded

141
Q

how can the distance of a far galaxy be determined by

A

brightness of supernova in the galaxy

142
Q

what is H0

A

hubble constant

143
Q

what is hubble constant

A

ration of the speed at which the galaxy is moving away from earth and its distance from earth v/d

144
Q

current estimate ofH0

A

2.2 x 10^-18 per second

145
Q

what equation represents the estimate of age of universe

A

d/v = 1/H0

146
Q

disadvantages of nuclear power

A
  • expensive
  • risk of nuclear meltdown
  • nuclear fuel is finite
  • produces radioactive waste which is harmful and lasts a long time
147
Q

how to correct long sightedness

A

convex lense

148
Q

how to correct near sighedness

A

concave lense

149
Q

what is wrong with people with far sightnedess

A

less curved or short eyeballs

150
Q

what happens in the eye with long sightedness

A

long-sighted has a narrower lens with a smaller focussing power so the light rays meet and form an image behind the retina and not on it

151
Q

what is wrong with an eye that has near sightedness

A

has a wider lens with a larger focussing power so the light rays meet and form an image in front of the retina and not on it

152
Q

what does converging lense

A

converging lens causes rays to converge before they reach the eye so image is formed on retina not behind it

153
Q

how can concave lense be used to fix near sightedness

A

causes the rays to diverge before they reach the eye, so the image is formed on the retina and not in front of it

154
Q

process of nuclear fission

A
  • neutron collides with unstable nucleas
  • nucleus splits into 2 daughter nuclei and two or three neutrons (products)
  • gamma rays also emitted
155
Q

what is nuclear fission

A

The splitting of a large, unstable nucleus into two smaller nuclei

156
Q

what is nuclear fusion

A

whe two light nuclei join to form a heavier nucleas

157
Q

where does energy come from nuclear fusion

A

The energy produced during nuclear fusion comes from a very small amount of a particle’s mass converted into energy
Therefore, the mass of the product (fused nucleus) is less than the mass of the two original nuclei (reactants)

158
Q

what are the initial stages of a star

A

nebula, protostar, stable star

159
Q

what is nebula

A

giant interstellar cloud of dust and gas

160
Q

what is a protostar

A

gravitational attraction within a nebula pulls the particles closer together until a hot ball of gas forms, known as a protostar
As the particles are pulled closer together the density of the protostar increases
This results in more frequent collisions between the particles which causes the temperature to increase

161
Q

what is a stable star

A

Once the protostar becomes hot enough, nuclear fusion reactions occur within its core
The hydrogen in the core of the star is converted into helium
Every fusion reaction releases heat and light which keeps the core hot
Once a star initiates fusion, it is known as a stable star
During this stage, the star is in equilibrium as the forces acting on it are balanced
Gravitational forces act inwards
This is an attractive force which pulls the outer layers inwards
Thermal pressure acts outwards
This is exerted by the expanding hot gases inside the star as energy is released during fusion

162
Q

life cycle of low mass stars

A

red giant, planetary nebula, white dwarf

163
Q

what is white dwarf

A

collapsed core of red giant

164
Q

what is planetary nebula

A

when helium in the core runs out, fusion cannot occur, star becomes unstable and core collapses under its own gravity. outer layers are ejected as planetary nebula

165
Q

life cycle of high mass stars

A

red super giant, supernova, neutron star (blackhole)

166
Q

when does star become red super giant

A

when helium dusion occurs

167
Q

red super giant:

A

after helium fusion, core starts to fuse helium to carbon and then successively heavier elements are formed. core collapses and expands repetedly as reactions start and stop

168
Q

what is supernova

A

fusion reactions inside the red supergiant cannot continue once iron is formed
The core of the star will collapse rapidly and initiate a gigantic explosion called a supernova
At the centre of this explosion, a dense body called a neutron star will form
The outer layers of the star are ejected into space forming new clouds of dust and gas (nebula)
The nebula from a supernova may form new stars with orbiting planets
The heaviest elements (elements heavier than iron) are formed during a supernova and are ejected into space
These nebulae may form new planetary systems

169
Q

what is neutron star (black hole)

A

In the case of the most massive stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole
A black hole is an extremely dense point in space that not even light can escape from

170
Q
A

Physics (6 decks)

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