things to memorise Flashcards
Estimate the mass of a person
70kg
Estimate the height of a person
150cm
Estimate the walking speed of a person
1 m/s
Estimate the speed of a car on the motorway
30 m/s
Estimate the volume of a can of a drink
300 cm^3
Estimate the density of water
1000 kg/m^3
Estimate the current in a domestic appliance
13A
Estimate the e.m.f. of a car battery
12V
Estimate the hearing range (frequency)
20Hz to 20000 Hz
Estimate the young modulus of a material
something x 10^11
Distance
Total length moved (no direction)
Displacement
Distance in a certain direction
Speed
Distance over time taken
Velocity
Displacement over time taken
SUVAT Equations?
v=u + at v^2= u^2 + 2as s=ut + 1/2at^2 s=vt - 1/2at^2 s = 1/2(v + u) x t
Acceleration of free fall
9.81 m/s^-2
Projectile motion
uniform velocity in one direction and constant acceleration in perpendicular direction
Newton’s first law
An object remains stationary or in uniform motion unless a resultant force acts upon it.
Newton’s second law
The rate of change of momentum is proportional to the resultant force and occurs in the direction of force.
Newton’s third law
Every force has an equal force that occurs in the opposite reaction forming an action - reaction pair
Mass
Measure of the amount of matter in the body
Weight
Force of gravitational attraction on a body
Momentum
mass x velocity
Force
m x a; change in momentum/time taken for change
Principal of conservation of momentum
When bodies in a system interact, total momentum remains constant provided no external force acts on the system.
Perfectly elastic collision
A collision in which the total momentum is conserved. A collision in which the total kinetic energy is conserved.
Two identical spheres collide elastically. Initially, X is moving with speed v and Y is stationary. What happens after the collision?
X stops and Y moves with the speed of V : relative velocity before collision = - (relative velocity after collision)
Perfectly inelastic collision
Total energy is conserved but Ek is converted into other forms of energy. Only momentum is conserved and the particles stick together after collision.
Force
rate of change of momentum
Density
Mass per unit of volume
Pressure
Force per unit area
Upthrust
An upward force exerted by a fluid on a floating or submerged object. Caused by the difference in pressure on the bottom surface and the top surface.
Frictional force
Force caused by the rubbing of two surfaces
- always opposes relative or attempted motion
- always acts along the surface
Viscous force
Force caused by motion of an object in a fluid
- only exists when there is motion
- magnitude increases with speed of the object
Centre of Gravity
Theoretical point through which all the weight of an object is assumed to act.
Couple
A pair of forces the same size that produce rotation
- same magnitude
- same distance from pivot
- opposite direction
Moment
Moment = force x distance from pivot (perp.)
Torque of a couple
Force x distance between forces
Conditions of equilibrium
Resultant force equals zero. Resultant rotational force (torque) is equal to zero.
Principle of moments
For a body to be in equilibrium, the sum of all clockwise moments must equal the sum of all anticlockwise moments about the same pivot.
Pressure in fluids
Volume of water = A x h
Mass of Water = density x volume = p x A x h
Weight of water = density x volume x gravitational force = p x A x h x g
Pressure = force/area = p x A x h x g/ A = p x g x h
Therefore pressure = pgh
Law of conservation of energy
The total energy of an isolated system cannot change - it is conserved over time. Energy cannot be made or lost just converted between different forms.
Work done by a force
W = F x s
Work done by an expanding gas
W = pressure x change in volume
Temperature of gas has to be constant.
Gravitational potential energy
W = m g h
Power
V x I; Work done / time taken
Efficiency
Useful energy output/total energy output x 100
Hooke’s Law
The extension produced by a spring is proportional to the applied force as long as the elastic limit is not exceeded: F = k x x
Parallel springs
ke = k1 + k2
Springs in series
1/ke = 1/k1 + 1/k2
Stress
Stress = Force / Cross-sectional area ( Pa)
Strain
Extension / original length ( no units )
Young Modulus
ration of stress to strain; units in Pa or N/m^2
Elastic deformation
When deforming forces removed, the subject returns to original form
Plastic deformation
When deforming forces removed, the subject returns to a stretched form
Strain energy
The potential energy stored by an object when it is deformed elastically W=1/2kx^2
Displacement (wave)
Distance of a point from its undisturbed position
Amplitude
The maximum displacement of a wave
Period
The time taken for 1 complete oscillation to occur
Frequency
Number of oscillations past a point per unit time
Wavelength
Distance from any point on the wave to the next exactly similar point
Wave speed
Speed at which the waveform travels in the direction of the propagation of the wave
Progressive waves
Transfer energy from one position to antoerh
Wave equation
v = lambda/ time and time= 1/f therefore v = lamba x frequency
Phase difference
Phase difference between two waves is the difference in terms of fraction of a cycle or in terms of angles.
Intensity
Power / Area; intensity is proportional to amplitude squared
Transverse waves
Waves in which the oscillations occur at 90 degrees to the direction of propagation.
Longitudinal waves
Waves in which the oscillations of the wave are parallel to the direction of propagation
Doppler effect
Observed freqeuncy = Frequency of source ( velocity of source wave / velocitiy of source wave (+-) velocity of source)
Electromagnetic waves
All travel at the speed of light : 3 x 10^8
Travel in free space ( no medium )
Can transfer energy
Transverse waves
What is the frequency of radio waves?
10^3
What is the frequency of microwaves?
10^-2
What is the frequency of infrared
10^-5
What is the frequency of visible light
0.5x10^-6
What is the frequency of ultraviolet waves?
10^-8
What is the frequency of X-ray?
10^-10
What is frequency of gamma ray?
10^-12
Interference
The formation of poitns of cancellation and reinforcement where 2 coherent waves pass each other
Coherence
waves having constant phase difference
Stationary wave
A stationary wave is formed when two progressive waves of the same frequency, amplitude and speed that are travelling in opposite directions superpose. Stationary waves store energy.
Node
Region of destructive superposition
Antinode
Region of maximum constructive superposition
Diffraction
The spreading of waves as they pass through a narrow slit
What is the equation for double slit interference?
lambda = ax/D a = split separation x = width of gap D = distance from slit to screen
What is the equation for diffraction grating?
d sin (theta) = n x lambda d= distance between successive slits = reciprocal of number of lines per meter theta = angle from horizontal equilibrium n= order number
What happens to a positive charge in an electric field?
Positive charge moves in the direction of the electric field; they gain Ek and lose Ep
What happens to a negative charge in an electric field?
Negative charge moves in opposite direction of the electric field: they lose Ek and gain Ep
Electric field strength
Force per unit of charge acting at a point. F/q or V/d
F is the force and q is the charge
V is p.d. and d is distance between parallel plates
Electric current
Flow of charged particles
Charge
Product of the current at that point and the time for which the current flows Q= I x t
Coulomb
Charge flowing per second pas a point at which the current is one ampere
Potential difference
The work required to move a certain coulomb of charge between two points.
Power
I x V
Ohm’s law
V = IR
Current carrying conductors - formula?
I = (nLAq) / (L/v) L = length of conductor A = cross-sectional area of conductor n = no. of free electrons per unit volume q = charge on one electron v = average electron drift velocity
What is the relationship between I and V for a metallic conductor?
Linear - V is proportional to I
What is the relationship between I and V for a filament lamp?
As volts go up the temperature goes up. This increases the vibration of ions, increasing the collisions of ions with electrons. This increases resistance. Straight line then curves off at the top
What is the relationship between I and V for a thermistor
As the voltage goes up, the temperature goes up. This releases electrons reducing resistance. Resistance which is V/I increases. Starts off straight and gradient gets steeper and steeper
What is the relationship between I and V for a diode
Low resistance in one direction and infinite resistance to the left of the origin - I = 0
Resistivity
R = pL/A
e.m.f.
The energy converted into electrical energy from other forms when a current passes through the power source.
Internal resistance
Resistance to current flow within the power source. Voltage across resistor = V= IR Voltage lost to internal resistance V=Ir Therefore e.m.f. E= IR + Ir E= I(R + r)
Kirchhoff’s second law
The sum of emfs in a closed circuit is equal to the sum of potential differences.
Kirchhoff’s first law
The sum of currents entering a junction is equal to the total sum of currents leaving a junction
Thermistor
A type of potential divider. Resistance decreases with increasing temperature.
Light Dependent resistor
Resistance decreases with increasing light intensity.
Potentiometer
A continuosly variable potential divider used to compare potential differences. Potential difference along the wire is proportional to the length of the wire.
What are the results of Rutherford’s gold scattering experiment?
A beam of alpha particles were fired at a thin gold foil:
- most particles pass straight through
- some are scattered slightly
- very few deflect at an angle greater than 90
Conclusion:
- All mass and charge concentrated in the centre of the atom
Nucleus is positively charged as a-particles are repelled
Isotope
Atoms of the same element with a different number of neutrons but the same number of protons
Random (radioactivity)
Impossible to predict and each nucleus has the same probability of decaying per unit time
Spontaneous (radioactivity)
Not affected by external factors such as the presence of other nuclei, temperature and pressure
Features of an alpha particle
-Helium nucleus
-42He (symbol)
+2 charge
4 relative mass
slow speed
penetration can be stopped by paper
highly ionizing
effect of magnetic field causes particle to deflect slightly
effect of electric field causes particle to attract to negative
Features of a beta particle
two types - positron B+ and electron B- 0-1e 0+1e -1 charge and +1 charge Fast movement speed can be stopped by few mm of aluminium low ionisation energy deflected greater by magnetic field than alpha particles attracted to opposite charge of the particle
Features of gamma radiation
electromagnetic no charge no mass speed of light few cm of lead very low ionisation power unaffected by electric and magnetic fields
a-decay
Loses a helium proton
B- decay
Neutron turns into a proton and an electron. An electron (0-1e) and antineutrino (00v with a line over it) are emitted
B+ decay
proton turns into a neutron and a positron. An electron and neutrino are emitted. neutrino shown by v with no line
Gamma decay
A nucleus changes from a higher energy state to a lower energy state through the emission of electromagnetic radiation ( protons)
Fundamental particle
a particle that cannot be split up into anything smaller
Quarks
Quarks are fundamental particles that make up protons and neutrons.
Up Quark charge?
u - +2/3
Down Quark charge?
d -1/3
Strange Quark charge?
s -1/3
Antiparticle
All quarks have antiparticles. The charge is just the opposite
Leptons
A part of elementary particles- electron family is part of this group. Electrons, positrons, antineutrinos and neutrinos
Hadrons
Part of composite particles. Hadrons —> baryones —> protons and neutrons
