Physics Flashcards
(203 cards)
1
Q
Define current
A
The rate of flow of charge, measured in amperes (A) and assigned I as its symbol
2
Q
Define potential difference
A
The driving force that move charge around a circuit, measured in Volts (V) and assigned symbol V
3
Q
Define resistance
A
Anything that sows the flow of charge, measured in Ohms ( Ω ), assigned the symbol R
4
Q
Current through a component depends on 2 things
A
- The components resistance (greater resistance = smaller current)
- The potential difference across the component (greater pd = larger current given a fixed resistance)
5
Q
Size of current is the same as…
A
Rate of flow of charge
6
Q
Charge (Coulombs, C) =
A
Current (A) x Time (s)
7
Q
Potential difference (V) =
A
Current (A) x Resistance ( Ω )
8
Q
Ohmic conductor (resistor at a constant temperature) I/V graph
A
Linear - as current will be directly proportional to charge - which means resistance doesn’t change
9
Q
Filament lamp I/V graph
A
Current increases so temperature of filament increases which means resistance increases - S shaped graph
10
Q
Diode I/V graph
A
High resistance in one direction, so current only flows in a single direction - gives a grapy of y = 2^x shape
11
Q
LDR resistance depends on
A
Light intensity
12
Q
LDRs have a lower resistance in
A
brighter light
13
Q
Where are LDRs used?
A
Automatic night lights
14
Q
Thermistor resistance depends on
A
Temperature
15
Q
Thermistors have a lower resistance in
A
Hotter temperatures
16
Q
Thermistors are used in
A
Thermostats
17
Q
Current in series
A
The same EVERYWHERE so I1 = I2
18
Q
Voltage in series circuits
A
Is shared between each component Vtot = V1 + V2
19
Q
Resistance in series circuits
A
Total resistance of components is the sum of their resistances Rtot = R1 + R2
20
Q
Current in parallel circuits
A
Sum of currents through each branch Itot = I1 + I2
21
Q
Adding a resistor in series…
A
Increases the total resistance of the circuit
22
Q
Voltage in parallel circuits
A
Is the same as the source of voltage V1 = V2 = Vtot
23
Q
Resistance in parallel
A
Total parallel resistance is less than the resistance of the smallest resistor
24
Q
Adding a resistor in parallel…
A
Decreases the total resistance of the circuit
25
Alternating current
Current that constantly changes direction and is produced by an alternating voltage - mains supply
26
Direct current
Current that always flows in the same direction - supplied by batteries
27
UK mains systems
AC supply, frequency of 50Hz and voltage around 230V
28
Electric shocks
A large potential difference is produced across the body which causes current to flow across the body
29
Energy transferred (J)
Charge flow (Q(Coulombs)) x Voltage (V)
30
Amount of energy an appliance transfers depends on
An appliance's power and how long an appliance is on for
31
Energy transferred (J)
Power (W) x time (s)
32
Power is the...
Energy transferred per second
33
Power rating is the...
Maximum safe power an appliance can operate at
34
Power (W)
Current (A) x Voltage (V)
35
Power (W) =
Current ^2 (A) x Resistance ( Ω )
36
Transformers
Step up - increase resistance
| Step down - decrease resistance
37
Why is transferring at a high current not efficient?
There would be a lot of energy to the thermal energy stores of the surroundings
38
How does something become charged?
Rubbing two insulating materials together to move electrons from one to the other which means both materials become electrically charged - charge will be equal and opposite. Only electrons move, positive charges don't
39
When do electric sparks occur?
Electric charge builds on an object which builds a p.d. between the object and the earth (which is at 0V) increases, when p.d. is big enough there is a spark
40
Electric fields around charged spheres
Carries from positive to negative
41
When field lines are close together...
The field is stronger
42
How do charged objects exert forces on each other in a electric field
They either attract or repel each other (non-contact force)
43
How is an alternating current generated?
Rotating generators to constantly change current direction
44
Current = (given charge and time)
Charge (C)/ Time (s)
45
NTC =
Negative temperature coefficient thermistor - non-linear resistors that alter resistance with temperature
46
Ideal diode
Allows current to flow in one way but not the other
47
Energy transfer (J, symbol Q) =
Current (I) x Time (s) x Voltage (V)
48
Magnetic field lines
Flow from north to south
49
What is a soft magnetic material?
Iron/ iron-nickel alloy - are easily magnetised/ demagnetised
50
Hard magnetic materials
Tungsten steel/ chromium steel - retain magnetism for long periods of time
51
What is induced magnetism?
Magnetic material placed in the field of a magnet - does not retain magnetism out of field
52
Define the electromagnetic effect?
A current carrying wire produces a magnetic field, noticed by the points of a compass (Right hand thumb rule)
53
What is an electromagnet?
A soft metal core made into a magnet by the passage of electric current through a coil surrounding it
54
What 3 things affect the strength of an electromagnet?
Strength of the core material (iron core is best), strength of the current and number of turns of the wire
55
The motor effect
A wire carrying a current in a magnetic field experiences a force
56
What is the left hand rule?
Force (thumb) Magnetic field (index) and current (middle finger)
57
What does the direction of a force depend on?
Direction of magnetic field and direction of the current
58
What factors can increase the magnitude of a force felt by a wire carrying a current?
Increasing the magnetic field strength, increasing wire length and increasing the current in a wire
59
Force (N) =
B (magnetic field strength in N/Am or T) x I (current) x Length (m)
60
How do electric D.C. motors work?
A force on a conductor in a magnetic field causes rotation in motors
60
How do electric D.C. motors work? (dynamo)
A force on a conductor in a magnetic field causes rotation in motors
61
How is the force on a conductor in a motor increased?
More coils on the wire, increased current, stronger magnet and reduced friction
62
What are electromagnets used in?
Motors, generators, electric bells, loudspeakers and headphones
63
How can you induce a voltage in a wire?
Using a changing magnetic field or by moving the wire in a magnetic field will induce a current to flow
64
How does an A.C. generator work? (alternator)
As the coil rotates, the p.d. is induced and the alternating current is produced
65
What is a split ring commutator?
Ring that constantly alters the direction of the flow of current - ensures spin on a dynamo
66
What does a current/ time graph look like for an alternator?
A transverse wave
67
What does a current/ time graph look like for a dynamo?
Camel humps
68
Applications of electromagnetic induction
Microphones - diagram over a permanent coil that moves from air pressure and in loudspeakers - similar to microphones
69
Vp / Vs =
Np / Ns
70
How does a transformer work?
A changing magnetic field induces a changing potential difference in the 2nd coil
71
If a transformer results in 100% total transfer of electrical power, what equation does it result in?
As P = IV, the following is formed: Vp x Ip = Vs x Is
72
What does voltage measure?
Measures the energy transferred by each Coulomb of charge that flows through a wire
73
Even though some power is lost to heat in transformers, the power to the primary coil must...
The power supplied to the second (Law of the conservation of energy)
74
A higher voltage on a transformer means
More efficient transfer
75
Scalar and vector
Single and double magnitude measurements respectively
76
Displacement
Distance travelled as the crow flies
77
Velocity
Speed in a given direction
78
Speed =
Distance (m) / Time (s)
79
Velocity
Change in displacement (m) / Time (s)
80
Acceleration =
Change in velocity (m/s) / Time (s)
81
In a distance time graph what does the gradient of the line equal?
Speed
82
In a distance time graph what does a horizontal line mean?
Stationary
83
In a distance time graph what does a straight slope equal?
Constant speed
84
In a displacement time graph what does the gradient equal?
Velocity
85
In a displacement time graph what does a horizontal line mean?
Stationary
86
In a velocity time graph how do you calculate the displacement?
Area under the graph
87
In a velocity time graph what does a horizontal line mean?
Constant velocity
88
In a velocity time graph what does a straight slope mean (upwards or downwards)?
Constant acceleration/ deceleration
89
V^2 - U^2 =
```
2as
V = final velocity (m/s)
U = initial velocity (m/s)
a = acceleration (m/s^2)
s = displacement (m)
```
90
Weight is the
Force of gravity of an object
91
Normal contact force =
Force exerted upon an object when in contact with another stable object (perpendicular to the surface)
92
Drag force
Resistance caused by motion of a body through a fluid that opposes the direction of oncoming flow (air resistance)
93
Friction
Force between 2 sliding surfaces
94
Magnetic force
Attraction/ repulsion of electrically charged molecules
95
Electrostatic force
Attraction/ repulsion based on electric charge
96
Thrust
Push force that causes acceleration in one direction
97
Upthrust
Resultant upwards force from complete/ partial submersion where the base has a greater pressure
98
Lift
Component force in a liquid that is perpendicular to the oncoming direction of flow
99
Tension
Pulling force that is transmitted axially by chain/ rope
100
How to calculate the magnitude and direction of a force?
Net force (opposites minus) and the strength of any force in an alternate direction
101
What do unbalanced arrows on a force diagram mean?
Unbalanced forces
102
Net force =
All forces acting on an object
103
Force / extension for a rubber band =
Non-linear as shape alters but not constantly
104
Force / extension graph for a rubber band
Non linear as stretch isn't constant
105
Force / extension graph for a spring
Linear initially but once force is too great the shape is changed permanently so becomes non-linear
106
Elastic extension
Changes shape under force but returns to original when the force is removed
107
Inelastic extension
Permanently changed in shape under movement of a force
108
Hooke's Law equation
Force = K (x)
```
K = spring constant (N/m)
x = extension (m)
```
109
Hooke's Law written
Strain in a solid is directly proportional to the applied stress within the elastic limit of the solid
110
Energy transferred in stretching (J - same as work done) =
1/2 K x^2
```
K = Spring constant (N/m)
x = Extension (m)
```
111
Energy transferred in stretching given only force and extension (J) =
1/2 F x
when F is the force applied in N, and x is the extension in m
112
Newton's 1st Law =
A body will remain at rest of in a state of uniform motion in a straight line unless acted upon by a resultant external force
113
Main property of mass
Resists change in motion (inertia)
114
Newton's 2nd Law
Force (N) = Mass (Kg) x Acceleration (m/s^2)
115
Newton's 3rd Law
If Body A exerts a force on Body B, then Body B exerts an equal and opposite force of the same type on Body A
116
Gravitational field strength on Earth?
10 N/ Kg
117
Weight =
Mass (Kg) x Gravitational field strength (N/ Kg)
118
What factors affect air resistance?
```
Mass (higher with a higher mass),
Surface area (more room for the working of air resistance) and acceleration due to gravity (works to balance to frictional force over time)
```
119
Momentum (Kg m/s) =
Mass (Kg) x Velocity (m/s)
120
Law of the conservation of momentum
Momentum of an isolated incident must remain constant, so momentum is conserved over time and not created or destroyed
121
Force is also equal to the rate of change of momentum according to Newton's 2nd Law - this gives what equation
Force (N) = (Mass (Kg) x Change in velocity (m/s)) / Change in time (s)
122
Work done =
Force (N) x distance moved in direction of force (m)
123
1J of work is done when...
1N of force causes movement by 1m - so work done can be measured in Nm
124
GPE (J) =
Mass (kg) x Gravitational field strength (N/Kg) x Height (m)
125
Kinetic energy (J) =
1/2 mass (Kg) x Velocity ^2 (m/s)
126
Power (W) =
Energy transferred (J) / Time (s)
127
Law of the conservation of energy
Total energy of an isolated system remains constant, so is conserved over time
128
Useful vs Wasted energy
Can/ cannot be usefully transformed for a respective use
129
Percentage efficiency =
(Useful output / total input) x 100 (given the same units)
130
What 4 factors affect the rate of conduction?
Temperature difference (bigger = higher rate), cross sectional area, length and time
131
What happens when a liquid is heated?
The molecule movement speeds up, sending them further apart, occupying a higher volume which lowers the density
132
What causes heated particles in a fluid to flow?
Convection - a result of temperature and density variations
133
What is thermal radiation?
Electromagnetic radiation generated by the thermal motion of particles in matter
134
Specific heat capacity definition
The energy (heat) required to raise the temperature of the unit mass of a given substance by a usually one degree Celsius
135
Specific heat capacity (J /kg C or K) =
Thermal energy (J) / Mass (Kg) x Temperature change (C or K)
This equation is the same as Q = mc∆t - where Q is the symbol for heat transfer, m is mass, c is SHC and t is time
136
Ideal gas behaviour
Random moving particles not subject to inter-particular interactions
137
Pressure on a gas volume
Constant for an ideal gas if kept at isothermal conditions
138
Latent heat of fusion
Enthalpy change resulting from providing energy, typically heat, to a specific quantity of substance to change its state from solid to liquid at a constant pressure
139
Latent heat of vaporisation
Amount of energy added to a liquid substance to form a gas
140
Density (g/cm^3) =
Mass (Kg) / Volume (cm^3)
141
Pressure (Pa or N/m^2) =
Force (N) / Area (m^2)
142
Hydrostatic pressure (N/m^2) =
Height (m) x Density (Kg/m^3 or g/cm^3) x Gravity (N)
143
How do waves transfer energy?
Without the net movement of water, disturbance causes the energy transfer
144
Transverse movement
Movement is perpendicular to the movement of energy
145
Longitudinal movement
Parallel to the movement of the wave
146
Compression and rarefaction
Close and loose packing respectively
147
Frequency
Number of waves per point per unit time
148
Period definition
Time for 1 particle on a medium to make 1 complete vibration per cycle
149
Frequency (Hz) =
1/ Period (s)
150
WaveSpeed =
Distance/ Time
151
Wavespeed (m/s) =
Frequency (Hz) x Wavelength (m)
152
Law of reflection
Angle of incidence = Angle of reflection
153
Specular and diffuse reflection
Flat surfaces and rough respectively
154
Refraction at a boundary
Change of wave direction the result of changed density
155
Wave speed from less to more dense
Slows down - so bends towards the normal
156
What property of waves is constant at a boundary?
FREQUENCY
157
What value is constant with regards to light?
Speed at 330 m/s
158
What happens to wavespeed from deep to shallow water?
Slows down towards normal with a shorter wavelength
159
What is the Doppler effect?
Change in the frequency of a wave in relation to an observer moving relating to the wave source.
Receding - Redshifted so lower frequency but longer wavelength
Approaching - Blueshift so higher frequency and smaller wavelength
160
Plane mirror ray diagram requirements
Upright and laterally inverted, same height object, as far behind as in front and virtual image
161
Vibrations release...
A sound wave
162
Can sound waves travel in a vacuum?
No - no particles to transfer energy
163
Larger amplitude =
Higher sound
164
Larger pitch =
Smaller frequency (no affect on volume)
165
Frequency is the same as
Pitch
166
Human hearing range
20Hz to 20,000Hz
167
Ultrasound definition
Sound waves released and a picture built up from the time taken to travel - used in sonar and medical imaging
168
Are EM waves transverse?
Yes - and travel at the CONSTANT speed of light in a vacuum
169
Order of EM waves from lowest frequency to highest
Radio, micro, IR, visible, UV, X-Rays and Gamma
170
Radio wave properties
Used in broadcasting and communications, can travel very long distances and are reflected off the upper atmosphere - Lowest energies, lowest frequencies with the longest wavelength
171
Microwave uses
Cooking food, can penetrate the atmosphere
172
Infrared uses
Heater and night vision equipment and television remote controls
173
Visible light uses
Human vision, photography and optical fibres
174
Ultraviolet use
Fluorescent lamps
175
X-Ray uses
Medical equipment, view internal structures (absorbed by more dense tissues)
176
Gamma ray uses
Sterilising food and medical equipment - Highly penetrative - Highest energy, highest frequency and shortest wavelength
177
Mnemonic for EM waves
Roman Men Invented Very Unusual X-Ray Guns
178
Hazards of EM waves
```
Microwaves - Internal heating of body tissues
Infrared - Heat/ burning
UV - Mutations causing cancer/ blindness
X-Rays - Mutations and cell death
Gamma rays - Mutations and cell death
```
179
Atomic number =
Proton number
180
Mass number =
Proton + neutron number
181
2 main features of radioactive emission
Emissions are from an unstable nucleus and random
182
Alpha emission
Emits a helium nucleus (^4/2 He)
183
Beta emission
Emits one electron
184
Gamma emission
No change - just a ray
185
What does Beta emission do to mass number?
+1
186
Alpha decay penetrating power and ionisation?
Low penetrating (stopped by paper) and highly ionising
187
Beta decay penetrating power and ionisation?
Medium penetrating (stopped by a layer of aluminium) and medium ionising
188
Gamma decay penetrating power and ionisation?
Very penetrating (stopped by a block of lead only) and weakly ionising
189
What decay can be reflected by electric fields?
Alpha and Beta because they are both charged (Gamma isn't)
190
How do Alpha and Beta behave in a magnetic/ electric field?
They experience a deflecting force - if not, they move in parallel motion
191
Sources of background radiation
Cosmic rays, rocks, radon gas, animals, medical uses and buildings
192
Radioactivity hazards inside the body
Alpha very dangerous as absorbed by cells, beta and gamma low risk as the pass right through
193
Radioactivity hazards outside the body
Alpha doesn't reach cells, beta and gamma penetrate and mutate cells
194
Half life graph
Activity/ time and demonstrate the RANDOM decay of a material - show how long taken for % of atomic nuclei in a substance to emit spontaneously
195
How to calculate number of half lives?
(1/2)^n
196
What do all conductors have?
At least some resistance
197
What does a neutron change into in Beta emission?
Proton
198
When is there not always an induced current in a conductor which is experiencing a change in
magnetic field?
When the conductor is not part of a complete circuit
199
What is red shift?
Further away = longer wavelength and faster moving = redshifted
200
Do sounds travel faster or slower in a solid?
Faster - closeness of particles
201
What doesn't change when medium changes?
Frequency - waves cannot be created or destroyed
202
Regarding a gear what is radius directly proportional to
Turning force transmitted
