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SS1: PHYSICS – 3RD TERM

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  1. Production of Electric Current | Week 1
    6 Topics
    |
    1 Quiz
  2. Electric Current | Week 2
    5 Topics
    |
    1 Quiz
  3. Electrical Resistance of a Conductor | Week 3
    5 Topics
    |
    1 Quiz
  4. Particulate Nature of Matter | Week 4
    5 Topics
    |
    1 Quiz
  5. Crystalline and Non-crystalline Substances | Week 5
    3 Topics
    |
    1 Quiz
  6. Elastic Properties of Solids | Week 6 & 7
    4 Topics
    |
    1 Quiz
  7. Fluids at Rest & in Motion | Week 8 & 9
    6 Topics
    |
    1 Quiz
  8. Solar Collector
    3 Topics
    |
    1 Quiz



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Lesson 2, Topic 5
In Progress

Electromotive Force (E.M.F)

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E.m.f in Series:

When cells are connected in series, the positive terminal of one is connected to the negative terminals of the other. With this arrangement, a larger emf is obtained in the circuit with improved current.

Screenshot 2022 05 25 at 12.43.38

Etotal = E1 + E2 + E3

rtotal = r1 + r2 + r3

Where r = the internal resistance of the cell.

E.m.f in Parallel:

For a parallel connection, all positive terminals are joined together and all negative terminals are joined together.

emf in parallel

The e.m.f of one of the cell is equal to the total e.m.f E1 = E2 = E3

Example 1:

A cell of e.m.f 1.5V is connected to a resistor of resistance 3Ω. Calculate the current flowing.

Solution:

Emf = 1.5V, R= 3Ω, I =?

V = IR

I = \( \frac{V}{R} \)

I = \( \frac{1.5 V}{3 \Omega} \)

I = 0.5A

Example 2:

A battery of emf 24v and internal resistance 4Ω is connected to a resistor of 32Ω. What is the terminal p.d of the battery?

Solution:

Whether you are asked to or not, always sketch a circuit diagram before solving any question on current electricity.

Screen Shot 2020 11 29 at 9.10.35 PM

First, calculate the current, I

I = \( \frac {E}{R + r} \)

= \( \frac {24}{32 + 4 } \)

= \( \frac {24}{36 } \)

= \( \frac {2}{3} \scriptsize A \)

or 0.67A

∴ Terminal p.d, V = IR

= 0.67 x 32

= 21.3v

Evaluation Question:

1. A cell of e.m.f 1.5V and internal resistance 2.5Ω is connected in series with an ammeter of resistance 0.5Ω and a load of resistance 7.0Ω. Calculate the current in the circuit.
2. A cell of e.m.f 1.5V is connected in series with a resistor of resistance 3.0Ω. A voltmeter connected across the cell registers 0.9V, calculate the internal resistance of the cell.

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