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Physics Equation List :Form 5
Wave
Oscillation
1
f =
T
f = frequency
T = Period
(Hz or s-1)
(s)
Displacement-Time Graph
•
Amplitude, Period and Frequency can be found from a Displacement-Time Graph
Wave
v= fλ
v = velocity
f = frequency
λ = wavelength
Displacement-Distance Graph
λ = Wavelength
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1
(ms-1)
(Hz or s-1)
(m)
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Interference
λ = Wavelength
ax
λ=
D
a = Distance between the two wave sources
x = Distance between two successive anti-node lines or node lines
D = Distance from the wave sources to the plane where x is
measured.
Summary
Electricity
Sum of charge
Q = ne
Q = Charge
n = number of charge particles
e = charge of 1 particle
Current
Q
I=
t
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Q = Charge
I = Current
t = time
2
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Potential Difference
W
V=
Q
V = potential difference,
W = energy
Q = charge
(V or JC-1)
(J)
(C)
V = potential difference,
I = Current
R = Resistance
(V or JC-1)
(A or Cs-1)
(Ω)
Ohm’s Law and Resistance
V = IR
Resistance
R=(
R = R1 + R2
1
1
1
+
+ ) −1
R1 R2 R3
Current
Series Circuit
Parallel Circuit
The current flow into a resistor = the current flow
inside the resistor = the current flows out from the
The current flow into a parallel circuit is equal to the
resistor
sum of the current in each branches of the circuit.
IA = IB = IC
I = I1 + I2
Example
If the resistance of the 2 resistors is the same, current
will be divided equally to both of the resistor.
In a series circuit, the current at any points of the
circuit is the same.
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Potential and Potential Difference
Series Circuit
Parallel Circuit
The sum of the potential difference across individual
resistor in between 2 points in a series circuit is equal
to the potential difference across the two point.
The potential difference across all the resistor in a
parallel circuit is the same.
V = V1 + V2
Example
V = V1 = V2
Example
Potential Difference and Electromotive Force
If we assume that there is no internal resistance in the cell, the potential difference across the cell is equal to
the e.m.f. of the cell.
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Electromotive Force and Internal Resistance
E = I (R + r)
E = V + Ir
or
E = Electromotive Force
r = internal resistance
V = potential difference,
I = Current
R = Resistance
(V)
(Ω )
(V or JC-1)
(A or Cs-1)
(Ω)
2 methods to find the internal resistance and electromotive force
a. Open Circuit – Close Circuit method
Open Circuit
Close Circuit
In open circuit ( when the switch is off), the In close circuit ( when the switch is on), the
voltmeter shows the reading of the e.m.f.
voltmeter shows the reading of the potential
difference across the cell.
•
With the presence of internal resistance, the potential difference across the cell is always
less than the e.m.f..
b. Linear Graph method
From the equation,
E = V + Ir
Therefore
V = -rI + E
Gradient od the grapf, m
= -internal resistance
Y intercept of the graph, c
= electromotive force
Electrical Energy
E = QV
E = Electrical Energy
Q = charge
V = potential difference
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(J)
(C)
(V or JC-1)
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Electrical Power
W
P=
t
P = IV
P=I R
2
V2
P=
R
(W or Js-1)
(J)
(s)
(A)
(V)
(Ω)
P = Power
W = Work done/Energy change
t = Time
I = Current
V = Potential difference
R = Resistance
Efficiency
Electrical efficiency =
output power
× 100%
input power
Electromagnetism
Root mean Square Value
Vrms =
Vp
2
Vrms = root mean square voltage
Vp = peak voltage
I rms =
Ip
2
Irms = root mean square current
Ip = peak current
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(V)
(V)
(A)
(A)
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Transformer
Input And Output Of A Transformer
Vs
N
= s
Vp N p
Vp = input (primary) potential difference
Vs = output (secondary) potential difference
Np = number of turns in primary coil
Ns = number of turns in secondary coil
(V)
(V)
Power In A Transformer
Ideal Transformer
V p × I p = Vs × I s
Vp = input (primary) potential difference
Vs = output (secondary) potential difference
Ip = input (primary) current
Is = output (secondary) current
(V)
(V)
(A)
(A)
Non-ideal transformer
Efficiency =
Vs I s
× 100%
Vp I p
Power Transmission
2Steps to find the energy/power loss in the cable
a. Find the current in the cable by the equation P=IV
2
b. Find the Power lost in the cable by the equation P=I R.
Electronic
Energy change of electron in an electron gun
Kinetic energy electrical potential
=
energy
gain
1 2
mv = eV
2
2eV
v=
m
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v = speed of electron
V = potential difference across the electron gun
e = charge of 1 electron
m = mass of 1 electron
7
(ms-1)
(V)
(C)
(kg)
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Cathode Ray Oscilloscope
Vertical scale = Y-gain control
Horizontal scale = Time base
Period = Time for 1 complete Oscillation
Frequency,
f =
1
T
Transistor - Potential Divider
Potential difference across resistor R1
=
R1
×V
R1 + R2
Potential difference across resistor R2
=
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R2
×V
R1 + R2
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Radioactivity
Alpha decay
A
A− 4
4
Z X ⎯⎯→ Z − 2Y + 2 He
Beta decay
Y+
A
A
Z X ⎯⎯→ Z +1
1
0
0
−1
e
n→11p + −10 e
Gamma emission
A
A
Z X ⎯⎯→ Z X
+γ
A = nucleon number
Z = proton number
Half-life
1
N = ( )n N0
2
N = Amount of radioisotope particles after nth half life.
N0 = Initial amount of radioisotope particles.
n = number of half life
Nuclear Energy - Einstein Formula
E = mc 2
m = mass change
c = speed of light
E = energy changed
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(kg)
(m s-1 )
(J)
9