Physics Final Exam: big pack Flashcards
Speed:
->the distance travelled per unit time
-if something is changing, it’s accelerating (near the Earth it is constant)
average speed = total distance/total time
s (m/s) = d (m) /t (s)
Velocity:
->speed in a given direction
Acceleration:
->change in velocity per unit time
acceleration = change in velocity/time taken
a (m/s^2)= v (m/s) -u/t (s)
Equation for the final speed:
(final speed)^2 = (initial speed)^2 + (2 x acceleration x distance)
v^2 = u^2 +2as
Distance-time graphs:
-the gradient is velocity
-negative gradient = returning back to the starting point
-a horizontal line = stationary
-if the distance = 0, it is back at the starting point
-curved line = velocity is changing, and it is accelerating
Velocity time-graphs:
-the gradient is acceleration
-negative gradient = deceleration
-if speed = 0, it is at rest
-horizontal line = constant speed
-area under the line = distance travelled
-curved line = acceleration is changing
Vectors:
have magnitude and direction
Scalars:
have just magnitude
Examples of scalar quiantities:
distance, speed, time, energy…
Examples of vector quantities:
displacement, velocity, acceleration, force
Effects of forces:
-Forces can change the speed, shape or direction of a body (measures in newtons (N))
eg: gravitational, electrostatic
Friction:
forces between two surfaces which impedes motion and results in heating
eg: air resistance is a form of friction
How to find the resultant force:
-add together if in the same direction
-subtracted if in the opposite direction
Newton’s first law:
States that an object has a constant velocity unless acted on by a resultant force
Newton’s second law:
force = mass x acceleration
f=ma
Mass & Weight:
-measure of how much matter is in an object, measured in kg
-weight is a gravitational force (the effect of a gravitational field on a mass)
weight = mass x gravitational field strength
W = mg
-gfs on Earth is 10N/kg
Terminal velocity:
-Initially, there is no air resistance and the only force acting on it is weight
-As it falls, it accelerates which increases its speed and hence air resistance
-This causes the resultant force downwards to decrease
-Therefore, the acceleration decreases
-Eventually they are equal, opposite and balance so there is no resultant force
-So, there is no acceleration and the terminal velocity is reached
Deformation:
-elastic deformation is when the object returns to its original shape when the load has been removed
eg: a spring being stretched
Hooke’s Law:
states that for a spring, F = kx where F is the force applied to the spring, k is the spring constant, and x is the extension
What does Linear and Non-Linear represent in a Hooke’s Law diagram?
Linear (straight line) force extension graph: -Elastic deformation following Hooke’s law:
-the point it stops being linera is called the limit of proportionality. From then on, it does not obey Hooke’s Law, and gradient becomes k
Non Linear (curved line) force extension graph:
-Deformation not following Hooke’s Law
-After this region, it will fracture
General waves properties:
-transfer energy and information without transferring matter
-the particles oscillate (vibrate) about a fixed point
Transverse waves:
-have peaks and troughs
-vibrations are perpendicular to the direction of travel
-eg: light
Longitudinal waves:
-consists of compressions (particles pushed together) and rarefractions (particles moved apart)
-vibrations are in the same direction as the direction of travel
-eg: sound
Amplitude:
the distance from the equilibrium position to the maximum displacement
Wavefront:
the front of a wave, or the same point on each wave
Frequency:
-the number of waves passing through a point per second
-frequency of a wave is equal to the reciprocal of the time period
-measured in Hertz (Hz):
frequency = 1/time period
f = 1/t
Wavelength:
The distance between two adjacent peaks on a wave
Time period:
the time taken for one complete wave to pass a point
Speed of wave:
speed = frequency x wavelength
v = f x λ
The Doppler Effect:
-if a wave source is moving towards to an observer, there will be a change in the observed frequency and wavelength due to the Doppler effect
-this is because wavefronts either get bunched together or spaced apart
eg: a siren of an ambulance is high-pitched as it approaches you, and low-pitched as it goes away
Reflection:
-all waves can be reflected when they travel from a medium of low optical density (such as air) to one much higher optical density (such as glass)
-the law of reflection says:
angle of incidence = angle of reflection
-frequency, wavelength, and speed are all unchanged
Refraction:
-all waves can be refracted, which is when the speed of a wave changes when it enters a new medium
-if the wave enters a denser medium, its speed decreases and it bends towards the normal
-if the wave enters a less dense medium, its speed increases and it bends away from the normal
-in all cases, the frequency stays the same but the wavlength changes. As a result, the velocity must change
Electromagnetic waves + spectrum:
-travel at the speed of light in vacuum
-can be reflected, refracted or diffracted
-speed = 3x10 (to the power of 8) m/s
(waves) RMIVUXG
low frequency-> high frequency + energy
longer wavelength<-shorter wavelength
Radio waves:
-red
used for radio and television communications
-long wavelength and are reflected by the ionosphere
Microwaves:
-orange
used for satellite transmissions and in cooking
-as they have a greater frequency (shorter wavelength) they are more penetrating so can pass through the ionosphere and penetrate deep into food
-can cause internal heating of body tissues-use an oven
Infrared radiation:
-yellow
used in heaters and night vision equipment
-can cause skin burns - protective clothing
Visible light:
-green
used in fibre optics and photography
Ultraviolet light: fl
-blue
used in fluorescent lamps
-can cause damage to surface cells and blindness - sunscreen + sun glasses
X-Rays:
-indigo
-used to observe internal structures of objects and materials + medical applications
Gamma radiation:
-violet
used in in sterilising food and medical equipment
can cause: cancer, mutation - led, concrete
Light:
transverse waves and can be reflected and refracted
Reflection of light: can be shown
can be shown when light reflects at a plane mirror and froms an image
-this can be represented by a ray diagram
What is the critical angle?
The angle of incidence which causes the angle of reflection to be 90º so that the light refracts onto the boundary
< c.a = reflection > c.a = refraction
refractive index = 1/ sin(critical angle)
n = 1/ sin(c)
Total Internal reflection:
-when the angle of incidence is greater than the critical angle, light is totally reflected within the same medium
-the light must also be travelling from a more optically dense medium into a less optically dense medium (eg: glass to air)
-light will keep reflecting
Optical fibres:
-used to transfer information by light, even when bent
-they are used extensively in medicines and communications
Sound:
longitudinal waves can be reflected and refracted
-the range of audible frequencies for a healthy human ear is 20 Hz to 20000 Hz
Speed of sound:
- make a noise
2.Record time for the echo - Use average speed formula (distance x 2 bc it’s going back and forth)
Oscilloscope:
an oscilloscope connected to a microphone can be used to display a sound wave and find its the frequency and amplitude
-greater amplitude of sound wave = the louder it is
-greater the frequency of a sound wave = higher pitch
Energy transfers: (8)
chemical, kinetic, gravitational, elastic, thermal, magnetic, electrostatic and nuclear
Mechanically:
e.g. when gravity accelerates an object and gives it kinetic energy
Electrically:
e.g. when a current passes through a lamp and it emits light and heat
By heating:
e.g. when a fire is used to heat up an object
By radiation:
when an object emits electromagnetic radiation
Energy:
is always conserved, total energy before = total energy after
efficiency = useful energy output/total energy input x 100%
-sankey diagrams can be used to represent the transfer of input energy into useful energy and wasted energy
Conduction:
-main method of thermal energy transfer in solids
-metals are extremely good at conducting heat
-non-metals are poor at conducting heat whilst liquids and gases are extremely poor (insulators)
-substance is heated, then atoms start to vibrate more and bump into each other-transferring energy from atom to atom
-delocalised electrons can collide with atoms helping to transfer vibrations through material and heat better
Convection:
-main way that heat travels through liquids and gases (can’t in solids)
-when a fluid (a liquid or a gas) is heated:
-molecules push eachother apart- making fluid expand
-this makes the hot fluid less dense than the surroundings
-hot fluid rises, and the cooler fluid replaces it
-eventually, hot fluid cools, contracts and sinks back down again
-resulting motion = convection current
Radiation:
-heat transferred by infrared
-the hotter the object, the more infrared radiation it radiates
-colour of object affects how well it emits and aborbs radiation
-black objects-best at emitting + absorbing radiation
-shiny objects-worst at emtting + absorbing radiation
Work:
is done when a force moves something through a distance
-work done = energy transferred
work done = force x distance
W =Fd
Conservation of Energy:
-when GPE turns into kinetic energy as It accelerates downwards
kinetic energy = 1/2 x mass x speed^2
gpe = mass x gravitational field strength x height
Power:
rate at which energy is transferred or the rate at which work is done in a given time
power = work done/time taken
P = W/t
Renewable energy:
energy which can be replenished as quickly a it is used
-all have potentionally infinite energy supply
- more costly
-less reliable
Non-renewable energy:
-resources can only produce energy some of the time (eg: when it’s windy)
-Fossil fuels: reliable, can produce large amounts of energy in a short time. Produces Green House gases + pollution
-Nuclear: reliable, produces no harm (above) a large amount of energy is produced from a small amount of fuel.produces dangerous radioactive waste
Energy transfers in the generation of electricity:
-in burning fossil fuels: chemical energy in chemical bonds
-in nuclear reactors: nuclear energy in atomic nuclei
-in a solar cell: light energy from the sun
-in geothermal nergy: heat energy from the Earth’s core
-in wind energy: kinetic energy from the moving wind
-in HEP: kinetic energy of moving waves
