a level physics

1. Waves:-
Displacement: It is the change in position of an oscillating particle from its rest or mean
position in a particular direction. It is a vector.
Amplitude: It is the magnitude of the maximum value of displacement. It is a scalar.
Phase Difference: If two oscillations are in step with one another, they are said to be in
phase with one another. Oscillations are said to be in antiphase if they are always moving in
opposite directions. For example; if the crest of one wave falls with the trough of another,
then they are said to be out of phase by 180 degrees.
Period: The time taken to complete one oscillation.
Frequency: The number of oscillations per unit time. It is measured in Hertz (Hz). 1 Hz is
one cycle per second.
Wavelength: It is the smallest distance between two points that are in phase with one
another.
(Wave) Speed: It is the speed with which crests of the wave move or the speed with which
energy is transferred. It is NOT the speed with which particles in the wave move.
The Transfer of Energy: The transfer of energy is due to a progressive wave, NOT a
standing/stationary wave.
Transverse Waves: A wave in which displacement of particles is perpendicular to the
direction of wave propagation, resulting in crests & troughs. E.g. light waves (the entire
electromagnetic spectrum)
Longitudinal Waves: A wave in which displacement of particles is parallel to the direction of
wave propagation, resulting in compressions & rarefactions. E.g. sound waves
Electromagnetic Waves: These are transverse waves. The displacement in the case of
electromagnetic waves is a variation in the electric & magnetic fields perpendicular to each
other.
Polarisation: As a result of the transverse nature of vibrations, transverse waves have an
additional property that is not possessed by longitudinal waves. The movement of particles
in transverse mechanical waves is at right angles to the direction of wave propagation. This,
however, still leaves many possibilities for the direction of the particle in 3D. Frequently,
oscillations take place in a transverse wave in many different directions, & the wave is said

2. to be unpolarised. If the oscillation does take place in only one direction, however, the wave
is then said to be polarized in that direction. That wave is then known as a plane-polarised
wave.
Stationary Waves: A stationary wave is produced because of superposition of two waves of
similar wavelength & amplitude, but travelling in opposite directions. A characteristic of a
stationary wave is that there are some parts of the wave where the amplitude is always zero.
The points are known as nodes. Halfway between the nodes, the amplitude is at its
maximum, & these points are called antinodes. Energy is NOT transferred in standing
waves.
Diffraction: The spreading of waves near an obstacle is called diffraction. If the width of the
opening is comparable with a single wavelength, the magnitude of diffraction is large as
compared with say, if the width of the opening was five wavelengths.
Diffraction Grating: It is a series of narrow parallel slits. If parallel monochromatic light
waves approach a series of narrow slits close to one another, the waves from each slit are
spread out over 180 degrees after passing the slits. It is the ability of a diffraction grating to
give a dark background, where the intensity is near zero, that makes it useful for examining
spectra.
Principle of Superposition Of Waves: When two waves of the same type with similar
frequency & speed are in phase with each other, their total amplitude on joining
together/adding together is the sum of their individual amplitudes.
Interference: When two waves superimpose, they cause interference. When the crests of
both waves fall on each other, constructive interference is achieved & the displacement of
particles is at its maximum value. If the crest of one wave falls on the trough of the other,
destructive interference takes place & the displacement of particles is at its minimum value,
or zero.
Coherence: If monochromatic light is used, only one wavelength is present, as compared to
if white light was used. Since speed & frequency are the same, all imperfections within the
wave occur simultaneously for both sources of the monochromatic light. Two waves
maintaining a constant phase difference are said to be coherent.
Fringe Width/Separation: The separation between one bright fringe & the next bright
fringe.
Conditions for Observing Two-Source Interference:
· The two waves should be of the same type. (Both transverse or longitudinal).
· They should almost similar wavelength or frequency.

3. · They should arrive at a point at the same time (superimposed).
· They should maintain a constant phase difference. (Coherent sources are required).
Electricity:-
Electric Field: It is the modified area or region around a charged object in which it can apply
an electrostatic force of attraction or repulsion on a test charge. Electric field strength is
force per unit positive charge.
Electric Current: It is the amount of charge flowing through a circuit per unit time or It is
the rate of flow of charged particles.
Ampere: If a charge of 1 Coulomb passes through an electrical component per second, then
the current maintained is 1 Ampere.
Potential Difference: The P.D across an electrical component is the energy converted from
electrical to other forms of energy when unit charge passes through it.
Volt: One volt is the P.D between two points in a circuit in which one joule of energy is
converted when one coulomb of charge passes from one point to the other.
Resistance: The ratio of P.D to the current for an electrical component at a particular time is
known as its resistance.
Ohm: A resistor has a resistance of one ohm if a P.D of one volt is to be maintained, to allow
a passage of one ampere of current.
Resistivity: The resistivity of a wire of a particular material is its resistance for unit length.
Coulomb: If a current of one ampere (6.25x1018 electrons) passes through a conductor, then
the charge flowed is one Coulomb or It is the amount of charge required to maintain a
current of one ampere in a conductor.
Ohm’s Law: The current through a metallic conductor is proportional to the P.D across it
provided that its temperature remains constant.
Thermistor (NTC): A specific type of resistor, in which, as temperature increases, the
magnitude of the resistor’s resistance decreases, & vice versa.
Electromotive Force: The e.m.f of any source of electrical energy is the energy converted
into electrical energy per unit charge supplied. It has the same unit as P.D; the volt.

4. E.m.f & P.D: While e.m.f refers to the amount of energy converted into electrical energy per
unit charge supplied, P.D refers to the amount of electrical energy converted into other
forms of energy per unit charge supplied. The e.m.f of a source is equal to the potential
difference across its terminals as the current approaches zero.
Effect of Internal Resistance on P.D & Output Power: The higher the internal resistance of
the battery/cell, the lower the terminal P.D, & hence, the lower the output power as well.
This is due to the equation V = E – Ir
Potentiometer: When a potential divider arrangement is used to compare e.m.fs of two
sources, it is known a potentiometer.
Kirchhoff’s First Law: The algebraic sum of the currents at a junction is zero. In other
words, charge cannot be created or destroyed.
Kirchhoff’s Second Law: Around any closed loop in a circuit, the algebraic sum of the e.m.fs
is equal to the algebraic sum of the P.Ds. In other words, each & every point in a stable
electrical circuit has a particular value of potential. Any gains in electrical energy of a charge
must be balanced by corresponding losses of energy.
Kirchhoff’s First & Second Laws are in correspondence & actually are an appreciation of the
Law of Conservation of Charge & the Law of Conservation of Energy respectively.