ELECTRIC CURRENT AND
DIRECT CURRENT CIRCUIT
3.2 RESISTIVITY AND OHM’S LAW
3.6 KIRCHHOFF’S LAWS
3.3 ELECTROMOTIVE FORCE (emf), INTERNAL RESISTANCE AND POTENTIAL
DIFFERENCE
3.4 ELECTRICAL ENERGY AND POWER
3.5 COMBINATION OF RESISTORS
3.7 ELECTRICAL MEASUREMENT DEVICES
3.1 ELECTRICAL CONDUCTION
Resistivity and Ohm’s law
Resistance (R)
Depends on:
- Type of material it is made
- Its length (L)
- Its cross-sectional area (A)
- Its temperature (T)
SI unit: Ohm (Ω) @ V/A
Conductivity, σ
Resistivity, ρ
- Known as specific resistance
- A good electric conductor have a very low resistivity
- Good insulators have very high resistivity.
- Depends on the length and cross-sectional area.
SI unit: Ohm meter (Ωm)
Ohm’s Law
Property which opposes or limits current
The voltage drop across a conductor, V is proportional to the current, I through
it if its physical conditions & temperature are constant
Electric current, I
Electric field or electric current:
+ve to -ve terminal
Electron flows:
-ve to +ve terminal
Current density, J
The direction of current density, J always in the same direction of the current I.
Electrical conduction in metal
: The magnitude of the drift velocity is much smaller than the random velocities of thefree electron.
Drift velocity of charges, Vd
Emf, ε and potential difference, V
Internal resistance of a battery, r
(open circuit)
Vr:potential difference acrossinternal resistance
Electrical energy, E
Power, P
The energy liberated per unit time in the electrical device.
SERIES CIRCUIT
PARALLEL CIRCUIT
Equivalent Resistance (RE):
RE = R1+ R2 + R3
Voltage(V):
V =V1 +V 2 +V3 +....+Vn
Current (I):
I = I1 =I2 =I3
Voltage(V):
V =V1=V2=V3
Current (I):
I = I1+ I2 + I3
Equivalent Resistance (RE):
1/RE = 1/R1 + 1/R2 + 1/R3 +....+1/Rn
Kirchhoff’s first law (junction or current law)
Kirchhoff’s second law (loop or voltage law
I3 = I1 +I2
For product of IR;
For emf, ε:
Ammeter (A)
Measures current
Voltmeter (V)
Measures voltage
Ohmmeter
Measure the resistance
Galvanometer
Shunt & Multiplier
Shunt (Pemirau)
A shunt resistor Rs in
parallel
Multiplier (Pendarab)
A multiplier resistor Rm in series