physics definitions Flashcards
1
Q
A physical quantity
A
A quantity that can be measured. Consists of a magnitude and a unit
2
Q
Oscillation
A
A complete to-and-fro motion of an object
3
Q
Period of a simple pendulum
A
Period of a simple pendulum is the time taken for one complete oscillation
4
Q
Scalar quantities
A
They are physical quantities that only have magnitude
5
Q
Vector quantities
A
Are physical quantities that have both magnitude and direction
6
Q
Speed
A
Distance moved per unit time
7
Q
Velocity
A
Rate of change of displacement
8
Q
Acceleration
A
Rate of change of velocity
9
Q
What does the gradient of a displacement-time graph give you?
A
Velocity of the object
10
Q
What does the gradient of a velocity-time graph give you?
A
Acceleration of the object
11
Q
How to find displacement?
A
Area under a velocity time graph
12
Q
When does an object achieve terminal velocity?
A
When weight = air resistance
13
Q
Newton’s first law of motion
A
States that every object will continue in its state of rest or uniform motion in a straight line, unless a resultant force acts on it.
This law is known as “inertia” - dependent on mass
14
Q
Newton’s second law of motion
A
States that when a resultant force acts on an object of a CONSTANT MASS, the object will continue to accelerate in the direction of the resultant force. Product of mass and acceleration gives the resultant force
F=ma
15
Q
Newton’s third law of motion
A
States that if body A exerts a force Fab on body B, body B will exert an equal and opposite force Fba on body A.
For every action, there’s an equal and opposite reaction
16
Q
Friction
A
Is the contact force that opposes or tends to oppose motion between surfaces in contact
17
Q
Mass
A
It’s the amount of matter in a body
18
Q
Weight
A
Weight of an object is the gravitational force or gravity acting on it
W=mg
19
Q
Gravitational field
A
Is a region in which a mass experiences a force due to gravitational attraction
20
Q
Gravitational field strength, g
A
Defined as the gravitational force acting per unit mass
21
Q
Inertia of an object
A
The reluctance of an object to change its state of rest or motion, due to its mass
22
Q
Density
A
Mass per unit volume
p=m/v
23
Q
Moment of a force
A
Is the product of the force and perpendicular distance from the pivot to the line of action of the force
24
Q
Principle of moments
A
When a body is in equilibrium, the sum of anti-clockwise moments about a pivot is equal to the sum of clockwise moments about the same pivot.
25
Centre of gravity
Is a point in which the weight of an object appears to act on
26
Stability
Is a measure of its ability to return to its original position even after being slightly displaced
27
The three types of equilibrium?
1. Stable equilibrium
2. Unstable equilibrium
3. Neutral equilibrium
28
What is stability affected by?
1. Base area
2. Center of gravity
29
Energy
It’s the capacity to do work
30
Principle of conservation of energy
States that energy cannot be created not destroyed, it can only be converted from one form to another. Total energy in an isolated system remains constant
31
Work done
Work done by a Constant force of an object is the product of the force and the distance moved by the object in the direction of the force
Work done = force x distance moved in the direction of force
32
Power
Rate of work done or rate of energy conversion
33
Pressure
Force acting per unit area
P= F/A
34
Temperature
Refers to how hot or cold an object is
35
Heat
Amount of thermal energy that is being transferred from a hotter to a colder region
36
Kinetic model of matter
States that tiny particles that make up matter are always in continuous random motion
37
Relationship between pressure and temperature?
Directly proportional
38
Relationship between pressure and volume
Inversely proportional
39
Relationship between temperature and volume
Directly proportional
40
Thermal energy
Always flows from a region of higher temperature to a region of lower temperature. Net flow of thermal energy only occurs when there is a difference in temperature
41
Conduction
Is the transfer of thermal energy through a medium without any flow of the medium itself
42
Convection
Is the transfer of thermal energy by means of convection currents in a fluid (liquid or gas), due to the difference in densities
43
Radiation
It’s the transfer of thermal energy in the force of electromagnetic waves such as infrared radiation without the aid of a medium
44
Heat capacity C
It’s the amount of thermal energy required to raise the temperature of a substance by 1K or 1 degree celcius
45
SI Unit for Heat Capacity C?
JK-1 or JC-1
46
Specific heat capacity c
It’s the amount of thermal energy required to raise the temperature of a unit mass (1kg) of a substance by 1K or 1 degree celcius
47
Unit for specific heat capacity?
Jkg-1K-1 or Jkg-1C-1
48
Latent heat
It’s the energy released or absorbed by a substance during a change of state, without a change in its temperature
49
Latent heat of fusion
The amount of thermal energy required to change a substance from solid to liquid state, without a change in temperature
50
SI Unit for latent heat of fusion
J (Joules)
51
SI Unit for latent heat of fusion
J (Joules)
52
Specific latent heat of fusion
The amount of thermal energy required to change a unit mass (1kg) of a substance from a solid to liquid state, without a change in temperature
53
SI Unit for specific latent heat of fusion?
Jkg-1
54
Latent heat of vaporisation
is the amount of thermal energy requires to change a substance from liquid state to gaseous state, without a change in temperature.
55
SI Unit for latent heat of vaporisation
J (Joules)
56
Specific latent heat of vaporisation
is the amount of thermal energy required to change a unit mass (1kg) of a substance from liquid state to gaseous state, without a change in temperature.
57
SI Unit for specific latent heat of vaporisation?
Jkg-1
58
First law of reflection
States that the incident ray, reflected ray, and the normal at the point of incidence all lie in the same plane
59
Second law of reflection
States that angle of incidence i is equal to the angle of reflection r (i=r)
60
Refraction
It’s the bending of light as light passes from one optical medium to another
61
First law of refraction
Incident ray, refracted ray, and the normal, all lie in the same plane
62
Second law of refraction
States that for two given media, the ratio of the sine of angle of incidence i to the sine of the angle of refraction r is a constant
sini/sinr = n
63
Critical angle c
Defined as the angle of incidence in an optically denser medium for which the angle of refraction in the optically less dense medium is 90 degrees
64
Total internal reflection
Is the complete reflection of a light ray inside an optically denser medium at its boundary with an optically less dense medium
65
Focal length
is the distance between the optical centre and the focal point
66
Source of a wave
Is a vibration or oscillation
67
What do waves do?
They transfer energy from one point to another without transferring the medium
68
Transverse waves
Are waves that travel perpendicular to the direction of the vibration
69
Longitudinal waves
Waves that travel parallel to the direction of the vibration
70
Amplitude A
of a wave is the maximum displacement of a point from its rest position
71
Wavelength
It’s the shortest distance between two points in a phase
72
Period T of a wave
It’s the time taken to produce one complete wave
73
Frequency f of a wave
Is the number of complete waves produced per second
Units: Hz
74
Wave speed
Is the distance travelled by a wave per second
75
Wavefront
It’s an imaginary line on a wave that joins all adjacent points that are in a phase
76
Sound
It’s a form of energy that is transferred from one form to another as a longitudinal wave
77
Echo
It’s the repetition of a sound due to the reflection of sound
78
Ultrasound
Is sound with frequencies above the upper limit of human range of audibility
79
Pitch is related by the?
Frequency of a sound wave. Higher the frequency, higher the pitch
80
Loudness is related to the?
Amplitude of a sound wave, the larger the amplitude, the louder the sound
81
Electric force
Is the attractive or repulsive force that electric charges exert on one another
82
Electric field
Is a region in which an electric charge experiences an electric force
83
Direction of an electric field
Is the direction of the force that would act on a small positive charge
84
The strength of an electric field
Is indicated by how close the field lines are to one another
85
Conventional current
Is in the opposite direction to electron flow
86
Electric current
Is the rate of flow of electric charge Q
I = Q/t
87
Electromotive force (emf) of an electrical energy source
Is the work done by the source in driving a unit charge around a complete circuit
88
Potential difference (p.d) across a component in an electric circuit
Is the work done to drive a unit charge through the component
89
Resistance R of a component
Is the ratio of the potential difference V across it to the current I flowing through it
V=IR
90
Ohms law
States that the current passing through a metallic conductor is DIRECTLY proportional to the potential difference across the component, provided that physical conditions such as temperature remains constant
91
Potential divider
Is a line of resistors connected in series but is used to provide a fraction of the voltage of a source to another part of the circuit
92
Input transducers
Are electronic devices that convert non-electrical energy to electrical energy
93
Magnetic materials
Are materials that can be attracted to a magnet
(COINS)
Cobalt
Iron
Nickel
Steel
94
Non-magnetic materials
are materials that cannot be attracted to a magnet
95
Magnetic induction
Is the process whereby an object made of a magnetic material becomes a magnet when it is near or in contact with a magnet
96
A magnetic field
Is the region surrounding a magnet, in which a body of magnetic material experiences a magnetic force
97
What is meant by an alternating current
An alternating current is an electric current that changes ita magnitude and direction of flow with time
98
Efficiency
Ratio of the useful power/energy output to the total power/energy input X 100%
99
Refractive index
It’s the ratio of the speed of light in vacuum to the speed of light in a medium
Or the ratio of the sine of angle of incidence in a vacuum to the sine of angle of refraction in a medium
100
What can radio waves be used for
-Radio broadcasting
- television communications
101
What can microwaves be used for
-microwaves, to heat food
-satellite television
- Global Positioning System GPS
- mobile phone networks
102
What can infrared radiation be used for
-remote controllers
- ear thermometers
- intruder alarms
- infrared photographs
103
What can visible light be used for
-optic fibres
- laser light
104
what can Ultraviolet rays be used for
- Sterilise surgical instruments
- artificial suntanning
- detection of forgery in bank notes
105
what can X rays be used for
- kill cancer cells (radiation therapy)
- used in diagnostic tools in medicine and dentistry to observe for cracks and fractures
- airport security, inspecting insides of luggages
106
what can Gamma rays
- sterilise medical equipment
- kill cancer cells
107
what happens From radio to gamma rays?
(R M I V U X G)
Wavelength decreases, frequency increases
108
Kinetic energy is always related to?
Temperature
109
Why should the fuse and switch be connected to the live wire? (USUALLY FUSE FIRST THEN SWITCH)
When the fuse is blown or switch is opened, the appliance will then be disconnected from the high potential of the live wire. This appliance will not be “live” as there is no current flowing through the appliance and it is safe to touch, prevents someone from getting an electric shock
110
What is the purpose of a live wire
It’s connected to a high voltage and delivers current to the appliance. This is the wire to which circuit breakers, fuses, and switches are fitted
111
What’s the purpose of the neutral wire
It completes the circuit by providing a return path to the supply for the current, it’s usually at 0 volts
112
What’s the purpose of an earth wire
It is a low resistance wire and it is usually connected to the metal casing of appliances
If an electrical fault results in the live wire touching the metal casing, the earth wire is able to allow large currents to flow to the ground, which has a much lower resistance than the person. Hence preventing an electrical shock.
113
Why is the earth wire usually thick?
Bigger cross sectional area = lower resistance
114
why is there an output voltage produced in the secondary coil?
because of the alternating current, it produces a changing magnetic field around it. this means that there is a change in magnetic flux linkage the secondary coil and hence by faradays law, an emf is produced
115
what’s the split ring commutator for?
it reverses the current direction in the coil every half a turn and allows the coil to constantly turn in ____(upward/downward) direction. third it rotates in an (anti clockwise / clockwise) direction continuously
116
what are slip rings for?
to allow firm contact between coil and the 2 carbon brushes such that there is constant contact to allow the current to flow to the external circuit. the direction of the induced current produced will be alternating
117
order of resistivity from lowest to highest
-silver
-copper
- aluminium
- tungsten
- nichrome
SCATN
strong clever awesome talented nice
118
what happens to the speed of light from a less dense to denser medium? how does it bend?
bends towards normal, speed of light decreases
119
what happens to the speed of light from a denser to a less dense medium? how does it bend?
bends away from normal, speed of light increases
120
explain conduction
conduction is the process by which thermal energy is transmitted through a medium caused by molecular vibrations.
when ___ it is heated, the atoms gain kinetic energy and vibrate faster about in their fixed positions. the atoms collide with the less energetic neighbouring atoms resulting in the transfer of kinetic energy from a region of higher temperature to a region of lower temperature. this process continues until they all possess the same amount of thermal energy
** thermal energy is transferred through the increase in vibration and hence the kinetic energies of the atoms**
*talk about how they’re closely packed and vibrate about their fixed positions**
121
why does conduction occur better in metals?
conduction is far better in metals because they contain many free electrons that are able to move freely among the atoms of the metal
(there is collision of the vibration of atoms and free moving electrons)
when heated, free mobile electrons gain energy and move vibrate and move more vigourously. since these mobile electrons are free to travel in spaces between the atoms to transfer energy
122
explain convection currents in liquids
if the air gains heat, it will expand and become less dense
if air does not gain heat, it’s considered as “colder air” which is denser than hot air
hot air rises and cold air sinks to replace the hot air, this sets up a convection current due to the difference in densities
this process repeats ( cold air gains heat bla bla bla)
thus there is a transfer of thermal energy from convection
123
factors affecting radiation?
surface temperature
- hotter an object, higher the energy emission
surface area
- larger s.a, higher rate of energy transfer
surface colour and texture
- rough, dull, black is a better emitter and absorber of infrared radiation
124
What does a current carrying conductor do
It produces a magnetic field around it
125
What happens when the current is reversed in a current carrying wire?
The direction of the magnetic field is reversed
126
What happens when current increases in a current carrying wire?
Strength of magnetic field increases
127
How the the strength of the magnetic field of a flat coil be increased?
Increase the current flowing through the coil
128
The magnetic field strength of a solenoid can be increased by
Increasing the current flowing through the solenoid
Increasing number of turns per unit length of the solenoid
Placing a soft iron core within the solenoid to concentrate the magnetic field lines
129
What is the motor effect?
It is when a current carrying conductor is placed in a magnetic field, the conductor will experience a force
130
What happens when we reverse the current or magnetic field in a current carrying conductor
The direction of the force on a current carrying conductor is reversed when we reverse the direction of current or magnetic field
131
What is FLHR used for
To find The direction of the force on a current carrying conductor in a magnetic field
132
Conductors carrying currents in the same direction
Attract
133
Conductors carrying currents in opposite directions
Repel
134
Electrons flow with current?
Opposite
135
The turning effect on a current carrying conductor can be increased by:
Increasing the number of turns in the wired coil
Increasing the current in the wire coil
136
The turning ever on a current carrying conductor in a DC motor can be increased by
Inserting a soft iron core into the coil
Increasing the number of turns in the coil
Increasing the current in the coil
137
Definition of electromagnetic induction
It is the process through which an induced emf is produced in a conductor due to changing magnetic field
138
Faradays law of electromagnetic induction
The magnitude of the induced emf in a circuit is directly proportional to the rate of change of magnetic flux in a circuit
139
Lenz law
States that the direction of the induced emf, and hence the induced current in a closed circuit, is always such that it’s magnetic effect opposes the motion or change producing it
140
An alternating current generator
Is a mechanical device that uses electromagnetic inducton to convert mechanical energy into electrical energy
141
A transformer
a device that can change a high alternating voltage to a low alternating voltage
142
What happens if we double the turns on the coil? (AC generator)
Doubling the number of turns would double the induced EMF ( max output voltage)
143
What happens if a e double the frequency/the speed of the turns in an AC generator
It will double the induced emf and also increase the frequency (period will be shorter)
