λ = Wavelength a = Distance between the two wave sources x = Distance between two successive anti-node lines or node l ines 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
I =
Q t
http://www.one-school.net/ notes.html
Q = Charge I = Current t = time
2
ONE-SCHOOL.NET
Potential Difference
V =
W Q
-1
V = potential difference, W = energy Q = charge
(V or JC ) (J) (C)
V = potential difference, I = Current R = Resistance
(V or JC ) -1 (A or) Cs Ω ) (
Ohm’s Law and Resistance
V
=
IR
-1
Resistance
R = (
R = R1 + R2
1 R1
+
1
+
R2
1 R3
)
1
−
Current Series Circuit
Parallel Circuit
The current flow into a resistor = the current flow inside the resistor = the current flows out from the resistor IA = IB = IC
The current flow into a parallel circuit is equal to the sum of the current in each branches of the circuit. 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.
http://www.one-school.net/ notes.html
3
ONE-SCHOOL.NET
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.
http://www.one-school.net/ notes.html
4
ONE-SCHOOL.NET Electromotive Force and Internal Resistance
E
=
I (R + r)
E =V
or
E = Electromotive Force r = internal resistance V = potential difference, I = Current R = Resistance
+
Ir
(V) ( Ω ) -1 (V or JC ) -1 (A or) Cs 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 voltmeter shows the reading of the e.m.f. •
In close circuit ( when the switch is on), the 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
http://www.one-school.net/ notes.html
5
(J) (C) -1 (V or JC )
ONE-SCHOOL.NET Electrical Power
P=
W
P = I 2R
P = IV
t
P=
V 2 R
-1
P = Power W = Work done/Energy change t = Time I = Current V = Potential difference R = Resistance
(W or Js ) (J) (s) (A) (V) Ω )
(
Efficiency
Electrical efficiency =
output power input power
×
100%
Electromagnetism Root mean Square Value
V rms
=
V p
2
V rms = root mean square voltage V p = peak voltage
I rms
=
I p
2
I rms = root mean square current I p = peak current
http://www.one-school.net/ notes.html
6
(V) (V)
(A) (A)
ONE-SCHOOL.NET Transformer Input And Output Of A Transformer
V s
V p = input (primary) potential difference V s = output (secondary) potential difference N p = number of turns in primary coil N s = number of turns in secondary coil
N s
=
V p
N p
(V) (V)
Power In A Transformer Ideal Transformer
V p × I p
=
V s × I s
V p = input (primary) potential difference V s = output (secondary) potential difference I p = input (primary) current I s = output (secondary) current
(V) (V) (A) (A)
Non-ideal transformer
Efficiency
V s I s
=
×
V p I p
100%
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 gain
1 2
=
mv
v=
electrical potential energy
2
=
eV
2eV
v = speed of electron V = potential difference across the electron gun e = charge of 1 electron m = mass of 1 electron
m
http://www.one-school.net/ notes.html
7
s-1
(m ) (V) (C) (kg)
ONE-SCHOOL.NET 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 R 1
R1
=
×
R1 + R2
V
Potential difference across resistor R 2
R2
=
R1 + R2
http://www.one-school.net/ notes.html
8
×
V
ONE-SCHOOL.NET
Radioactivity Alpha decay A 4 A − 4 Z X ⎯⎯→ Z − 2Y + 2 He
Beta decay A A Z X ⎯⎯→ Z +1
Y
1 0
+
0 e −1
n→11 p + 10 e −
Gamma emission
A A X ⎯⎯→ Z Z X + γ A = nucleon number Z = proton number Half-life
N
=
1
n
( ) N 0 2
N = Amount of radioisotope particles after nth half life. N 0 = 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
