Before conducting any experiment, follow these steps:

1. Understand the aim – Know what you are investigating and what results you expect
2. List all materials – Gather everything you need before starting
3. Draw a circuit diagram – Use standard symbols for electrical components
4. Set up carefully – Connect wires neatly; use a ruler for straight connections
5. Check connections – Have your teacher verify the setup before switching on
6. Record observations – Write down readings immediately in a table
7. Calculate and conclude – Use your data to answer the experiment questions

Measuring Electromotive Force (e.m.f) and Potential Difference (p.d)

Aim: To measure the e.m.f. of a cell and the p.d. across a conductor.

Materials: Dry cell (1.5 V), voltmeter, bulb, two switches, connecting wires.

Procedure:

1. Connect the circuit as shown in the diagram
2. Close switch S₁ only – this is when no current flows. The voltmeter reading equals the cell's e.m.f
3. Close both switches S₁ and S₂ – current flows through the bulb. The voltmeter now reads the p.d. across the bulb
4. Record both readings and compare them

Key observation: The voltmeter reading drops when current flows because the cell has internal resistance.

Investigating Ohm's Law

Aim: To determine the relationship between potential difference (V), current (I), and resistance (R).

Materials: DC power supply or 1.5 V cell, ammeter, bulb, voltmeter, rheostat, switch, connecting wires.

Procedure:

1. Set up the circuit
2. With the switch open, record the initial readings
3. Close the switch and adjust the rheostat to obtain different p.d. values (0.2 V, 0.4 V, 0.6 V, etc.)
4. For each p.d., record the corresponding current
5. Plot a graph of V against I

Expected result: For a conductor at constant temperature, V is directly proportional to I. The graph is a straight line through the origin, demonstrating Ohm's law: V = IR.

Investigating Resistors in Series and Parallel

Aim: To investigate the effective resistance for resistors connected in series and in parallel.

Materials: Two dry cells (1.5 V each), connecting wires, bulbs.

Procedure:

1. Connect one bulb (A) to the cells in series. Observe its brightness
2. Connect another bulb (B) in series with A. Observe the change in brightness
3. Now connect bulb B in parallel with bulb A. Observe the brightness

Observations:

• Series connection: Adding more bulbs reduces brightness because total resistance increases, reducing current
• Parallel connection: Each bulb maintains the same brightness because the p.d. across each remains constant

Determining Internal Resistance of a Cell

Aim: To determine the e.m.f. (E) and internal resistance (r) of a cell.

Materials: A cell, standard resistors (2–10 Ω), ammeter, switch, connecting wires.

Procedure:

1. Connect the circuit with the cell, ammeter, switch, and resistor R
2. Set R = 10 Ω, close the switch, and record the current I
3. Repeat for R = 8 Ω, 6 Ω, 4 Ω, and 2 Ω
4. Record results in a table

5. Plot a graph of R against 1/I
6. From the graph: the slope equals E (e.m.f), and the vertical intercept equals r (internal resistance)

Formula: E = I(R + r), which rearranges to R = E(1/I) – r

A cell with e.m.f. 1.5 V is connected to an external resistor of 3 Ω. If the terminal voltage falls to 0.6 of the e.m.f when current flows, calculate the internal resistance of the cell.

Solution

Given: E = 1.5 V, R = 3 Ω, V = 0.6E = 0.6 × 1.5 = 0.9 V

Using: E = V + Ir

First find current: V = IR, so I = V/R = 0.9/3 = 0.3 A

Now find internal resistance: E = V + Ir 1.5 = 0.9 + 0.3r 0.3r = 1.5 - 0.9 = 0.6 r = 0.6 ÷ 0.3 = 2 Ω

Therefore, the internal resistance of the cell is 2 Ω.

Classifying Magnetic and Non-magnetic Materials

Aim: To classify materials as magnetic or non-magnetic.

Materials: Bar magnet, knife, blade, copper rod, paper, glass rod, iron nail, wooden toothpick, chalk, aluminium foil, lead pencil, sand.

Procedure:

1. Bring each material close to the bar magnet
2. Observe whether it is attracted or not
3. Record your observations

Result: Materials containing iron, nickel, or cobalt (such as the knife blade and iron nail) are attracted – these are magnetic materials. Materials like copper, paper, wood, and glass are not attracted – these are non-magnetic.

Magnetising a Steel Rod

Aim: To magnetise a steel rod using the single-touch method.

Materials: Steel rod, bar magnet, pins.

Procedure:

1. Place the steel rod on a flat surface
2. Using the north pole of the bar magnet, stroke the rod from one end to the other in the same direction
3. Repeat about 10 times
4. Test the rod by hanging pins from it

Important notes:

• The pole produced at the end where you finish stroking is opposite to the pole of the magnet used
• Wide loops during stroking give better magnetisation
• If the magnet can hold many pins, it has reached saturation

Investigating Light Reflection and Refraction

Materials: Torch, cardboard with slits, plane mirror, curved mirrors, triangular prism.

Procedure:

1. Reflection: Shine light on a plane mirror and observe the angle of incidence equals the angle of reflection
2. Refraction: Pass light through a triangular prism and observe how white light splits into colours (dispersion)

Demonstrating Static Electricity

Materials: Glass rod, plastic ruler, cloth, small pieces of paper.

Procedure:

1. Rub the glass rod with cloth
2. Bring it near small paper pieces
3. Observe that the paper pieces are attracted to the rod

Explanation: Rubbing transfers electrons, creating opposite charges that attract neutral objects.

In Tanzania, understanding electricity experiments helps you use appliances safely at home. For example, when a fuse blows in your house (perhaps due to overloading too many appliances like a heater and iron used together), knowing how series and parallel circuits work helps you understand why the fuse protects the wiring. If a 240 V, 1000 W iron draws about 4.2 A, using a 5 A fuse is appropriate – it melts and cuts the circuit before the wiring overheats and causes a fire. This practical knowledge is essential for electrical safety in Tanzanian homes.