Download PHS102 Lecture 18 Sep 2014 DLI Block 2 2nd Floor

DR. A. O. ADEWALE
Course Outline:
Electrostatics, potential and capacitance, dielectrics, production and measurement
of static electricity. Current, Ohm’s law, resistance and resistivity, heating,
Galvanometers, Voltmeters and Ammeters.
D.C. circuits, sources of emf and currents, Kirchhoff’s laws. Electrochemistry. The
Earth’s magnetic fields and induction. Faraday’s and Lenz’s Laws. Force on a
current carrying conductor. Biot-Savart law. Flemmings right and left-hand rules,
motors and generators.
Cells in Series and Parallel
 When two or more cells are in series, with the positive terminal of one
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connected to the negative terminal of another, then the total e.m.f. is
given as,
E = E1 + E2 + E3 +…
and the total internal resistance is
r = r1 + r2 + r3 +…
If one of the cell, say e.m.f. E3, is connected in opposition with the
others, then
E = E1 + E2 - E3 +…
but the total internal resistance remains unaltered.
When similar cells are in parallel, then total e.m.f. = E, the e.m.f. of any
one of them. The internal resistance r is given by 1 1 1 1
    ...
where r1 is the internal resistance of each cell.
r r1 r2 r3
Example
E = 1.5 V + 1.5 V = 3.0 V
E = 20 V - 12 V = 8 V
E = 12 V
Current in a typical circuit
E
I
Rr
Terminal p.d
V  IR 
ER
Rr
Example
 Consider the circuit diagram in Figure 13.15. Calculate
the terminal p.d. across AB.
Class Work
The figure shows a battery of 12 V and negligible
internal resistance connected to three resistors.
Calculate the p.d. V across the 6 Ω resistor and the
current passing through the 8 Ω resistor.