THIRD TERM E-LEARNING NOTE
THIRD TERM SCHEME OF WORK
1 Electric Circuit (DC).
2 Resistors and Cells in Series and Parallel.
3. Electrical Energy and Power
4. Safety Device – Fuse
5. Atomic Structure, Diffusion and Osmosis
6. Crystal Structure of Matter – Amorphous and Crystalline Substances
7. Surface Tension
8. Capillarity
9 Elasticity
10. Energy Stored in an Elastic Material
11. Revision
12. Examination
WEEK 1
TOPIC: ELECTRIC CIRCUIT
CONTENT: Definition and functions of electric circuit and its components
Definition of some physical quantities in dc circuit
Verification of ohm’s law
Before explaining electric circuit, let us define some terms
- Conductors: They are materials which allow electrons to pass through them easily e.g. metal, graphite, acids, salt solution etc.
2. Semi conductors: They are materials whose resistivities is mid way between
good conductors and insulators e.g. germanium, silicon etc
3. Insulators: They are materials which do not allow electrons to pass through
them e.g. paper, plastic, glass, oil, cotton, dry hair, polythene etc
Electric Circuit : An electric circuit is a complete path provided for the flow of electric current. The circuit diagram below is a symbolic representation of such circuit.
Functions of dc circuit components
- cells are chemical devices which produces electric force/pressure that pushes the current to flow.
- Switch / key is a device used to start or stop the current flow.
- Ammeter measures the electric current flowing in a circuit
- Voltmeter measures the potential difference across the terminal of a load
- Rheostat varies the flow of current
- Resistor is a component that limits or regulate the flow of electric current
EVALUATION
- Define electric circuit
- State the functions of the components that make up a circuit
Definitions of some physical quantities
Electric Current (I): it is the measure of the rate of movement (flow) of charged particles along an electrical conductor (a circuit). It is simple electric charge (Q) in motion which consists of moving electrons.
I = Q/t ____________ (1a) where t – time (s)
Q = It ……………… (1b)
Potential Difference (V): Potential difference between two points in a circuit is the work done (W) when one coulomb of charge moves from one point to another.
W = Q (VB – VA) = QV ____________ (2a)
V = W/Q ………………………………(2b)
Electromotive Force (E): E.M.F of a cell is the p.d between the terminals of the cell when it is not delivering any current to the circuit.
Internal Resistance (r): r of a cell is the resistance offered by the electrolyte to the motion of the current.
Resistance (R): R is the ratio of the p.d across the conductor to the current flowing through it.
Ohm’s Law
Ohm’s law states that the electric current in a given metallic conductor is directly proportional to the potential difference applied provided that the temperature and other physical factors remain constant i.e V α I
Verification of ohm’s law.
Aim: To show that metallic/ohmic conductor obey ohm’s law
Apparatus: voltmeter, ammeter, rheostat, battery, key, pieces of wire and ohmic conductor x
Procedure: set up the apparatus as shown above
Observation: As the rheostat is been varied, the reading of the voltmeter is also changing. Also, the current in the ammeter is increasing with increase in potential difference.
Slope = ∆V/ ∆I = R
Where R is the constant of proportionality and it is called resistance (R)
Conclusion: ohmic conductors obey ohm’s law.
i.e. V = IR______________ 3(a)
I = V/R_____________ 3(b)
R= V/I _____________ 3(c)
NB : The relationship between I, E, R & r is that
I = E / R + r = V/R ……………4
EVALUATION
1. Define the following terms (a) Electric current (b) Potential difference (c) Internal resistance
2. Describe an experiment to verify ohm’s law
Reading Assignment : Read more on electric circuit – New school physics (pg 77 – 80)
WEEKEND ASSIGNMENT
- The SI unit of electric current is (a) ampere (b) volts (c) ohm’s (d) coulomb
- The SI unit of electric charge is (a) ampere (b) volts (c) ohm’s (d) coulomb
- The SI unit of potential difference is (a) ampere (b) volts (c) ohm’s (d) coulomb
- The SI unit of resistance is (a) ampere (b) volts (c) ohm’s (d) coulomb
- Ohm’s law states that (a) V=IR (b) Q=It (c) R=IV (d) W=QV
THEORY
1. Define the following terms (a) Electric current (b) Potential difference (c) Internal resistance
2. Describe an experiment to verify ohm’s law