Summarized notes for electricity and waves chapters in physics AS and A level

1. WAVES
Describing progressive waves
A periodic disturbance that transfers energy without transferring matter.
Transverse waves
The oscillations are perpendicular to direction of energy.
Speed, freq., & period of waves
Wave speed, v = freq., f x wavelength Freq. =
1
T
Wave equation
Wave intensity
Intensity (Wm^-2) =
power
area
Intensity directly
proportional to A^2
Longitudinal waves
The particles oscillate in the direction parallel to energy transfer
Regions of compression = molecules close together
Regions of rarefaction = molecules further apart
The Doppler Effect
The change is wave freq. with relative motion of a source and an observer

2. The electromagnetic spectrum
c = f λ
Electromagnetic waves in free space
Polarization
Phenomenon associated with only transverse wave.
Plane polarized- transverse waves which has oscillations only in one plane.
Polarizing light
Polarizing filter: made of material such as polaroid that only
allows light polarized in one particular plane to pass thru.
The direction of polarization allowed by the filter is called the
axis of polarization of the filter

3. Malu’s law states that the intensity of light
transmitted thru a polarizing filter is related to the
initial intensity, of polarizes light incident on the
filter and the angle between the polarization of the
light and the axis of polarization of the filter by
𝐼=𝐼0cos2𝜙

4. SUPERPOSITION
Superposition & stationary waves
Superposition of waves
Principle: the vector sum of the displacement of two overlapping waves of the same type gives the resulting
displacement
Stationary waves
Wave that occurs in a closed system, which does not travel; it has nodes and antinodes of min. and max.
amplitude; the wave does not transfer energy outside the closed system
Nodes have 0 amplitude and antinodes have
max. amplitude
Diffraction
The spreading out of waves when they pass
an edge of an obstacle or pass thru a gap
between obstacles.

5. Coherence & interference
Waves are said to be coherent if they have:
~ the same wave form ~ constant phase difference
~ the same freq. or the same wavelength
Two-source interference
If two sources of waves are coherent and quite close together, they will produce interference
Interference is the result of superposition of waves from two or more coherent sources
Constructive
Destructive

6. The diffraction grating
A series of equally spaced, parallel slits thru which the light can pass
n𝜆=𝑑𝑠𝑖𝑛(𝜃)
d =
1
N

7. ELECTRICITY
charge (C) = current (A) x time (s)
I = Anvq
V =
W
Q
P =
W
t
P = VI
V = IR
R =
pL
A
P = I^2R
FORMULAS
Ohm’s law: for a conductor at constant temp.
the p.d across the conductor is directly
proportional to the current passing thru it,
provided that the physical conditions remain
constant
Kirchhoff’s laws
First law: the algebraic sum of the currents at a junction is zero
I(A) = I(B) + I(C)

8. Second law: the algebraic sum of the p.d around any complete loop in a circuit is zero
Electromotive force & internal resistance
The energy transferred per unit charge that it drives around a complete circuit
E.M.F (volts) =
Work done by source (J)
Charge (coulombs)
1.5 V
1.5 V
1.5 V
E = Ir + IR