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Electric Cell
Uses of Electricity
- We use electricity for many tasks:
- Operating pumps to lift water
- Lighting homes, roads, offices, and markets
- Helps us work at night by lighting up places
Power Source
- Electricity comes from a power station
- Sometimes, electricity supply fails or is unavailable
- In such cases, we use torches for light
- Question: Where does a torch get electricity from?
Electric Cell
- Provides electricity to the torch bulb
- Used in:
- Alarm clocks
- Wristwatches
- Transistor radios
- Cameras
- Features of an electric cell:
- Small metal cap on one side (positive terminal)
- Metal disc on the other side (negative terminal)
- Produces electricity from chemicals inside
- Needs replacement when chemicals are used up
Torch Bulb
- Glass outer case with a metallic base
- Inside the glass case:
- Thin wire in the middle (filament)
- Filament gives off light
- Filament supported by two thicker wires
- One thick wire connected to the metal case
- Other thick wire connected to the metal tip at the base
- Two terminals at the base:
- Metal case
- Metal tip
Safety Note
- Danger Signs: Warning of electric danger on poles and substations
- Handling electricity carelessly can cause injury or death
- Portable generators are also dangerous
- Use only electric cells for activities
Activity: Examining a Torch Bulb (click here)
- Look inside a torch bulb
- Notice the thin wire (filament)
- Observe which part glows when the torch is on
- Understand the connections and terminals in the bulb
Important Caution
- Never join the two terminals of an electric cell without a switch and a device like a bulb
- This causes the chemicals in the cell to be used up quickly
- The cell will stop working
Connecting a Bulb to an Electric Cell
Lighting Up a Bulb
- Let’s learn how to make a bulb light up using an electric cell.
Activity 2: Connecting Wires
- Materials Needed:
- Four lengths of electric wire with different colored coverings.
- Steps:
- Remove plastic covering from the ends of each wire.
- Expose the metal wires.
- Attach wires to the cell and bulb as shown in Fig. 9.3 and Fig. 9.4.
- Use tape or rubber bands to fix wires.
- Experiment:
- Connect the wires in six different ways (Fig. 9.5 a to f).
- Check if the bulb glows for each arrangement.
- Note “Yes” or “No” in your notebook.
Understanding the Results
- Compare the arrangements where the bulb glows with those where it doesn’t.
- Reasoning:
- If the bulb does not glow, there might be a break in the connection.
Electric Circuit
What is an Electric Circuit?
- Connecting the two terminals of an electric cell to a bulb completes a path.
- This path allows electricity (current) to flow.
- Complete Path: This is called an electric circuit.
How Current Flows
- Current flows from the positive terminal to the negative terminal of the cell.
- When connected properly, current flows through the filament of the bulb, making it glow.
Troubleshooting: Fused Bulbs
Why Bulbs Fuse
- Sometimes, a bulb doesn’t glow because it is fused.
- Fused Bulb: Filament inside is broken.
- Break in Filament: No current can flow, so the bulb doesn’t light up.
Making a Torch
Activity 3: DIY Torch
- Materials Needed:
- Torch bulb
- Piece of wire
- Steps:
- Remove plastic covering at the ends of the wire.
- Wrap one end of the wire around the bulb’s base.
- Fix the other end to the negative terminal of the cell.
- Touch the bulb’s base tip to the positive terminal.
- Observation:
- The bulb glows when the base tip touches the positive terminal.
- Moving the bulb away turns it off, similar to a torch switch.
Electric Switch
We learned about a simple switch for our homemade torch. Let’s make an easier switch for our circuit.
Activity 4: Making a Simple Switch
Materials Needed:
- 2 drawing pins
- Safety pin (or paper clip)
- 2 wires
- Small sheet of thermocol or wooden board
Steps:
- Insert a drawing pin into one end of the safety pin and fix it on the thermocol sheet.
- Ensure the safety pin can rotate freely.
- Fix the other drawing pin on the thermocol sheet so the free end of the safety pin can touch it.
- Connect an electric cell and a bulb to this switch.
Observation:
- When the safety pin touches both drawing pins: The bulb glows. This means the circuit is complete, and the switch is ‘on.’
- When the safety pin does not touch the other drawing pin: The bulb does not glow. This means the circuit is incomplete, and the switch is ‘off.’
Conclusion:
- A switch either completes or breaks a circuit.
- Home switches work on the same principle but have a more complex design.
Electric Conductors and Insulators
We use metal wires to make circuits. What if we used a cotton thread instead?
Activity 5: Testing Conductors and Insulators
Activity 5: Testing Conductors and Insulators
Materials Needed:
- Samples of various materials (coins, cork, rubber, glass, keys, pins, plastic scale, wooden block, aluminum foil, candle, sewing needle, thermocol, paper, pencil lead)
- The electric circuit from Activity 4
Steps:
- Disconnect the switch, leaving two free wire ends.
- Touch the free ends of the wires together. The bulb should light up.
- Test each material by touching the free ends of the wires to the ends of the sample.
Observation:
- If the bulb glows: The material is a conductor (e.g., metals).
- If the bulb does not glow: The material is an insulator (e.g., rubber, plastic).
Conclusion:
- Conductors: Allow electric current to pass (e.g., copper, aluminum).
- Insulators: Do not allow electric current to pass (e.g., rubber, plastic).
- Importance: Conductors are used for wires; insulators are used for safety covers.
Caution:
- Your body conducts electricity. Be careful with electrical appliances.
Chapter Summary:
- An electric cell is a source of electricity.
- An electric cell has two terminals: positive (+ ve) and negative (– ve).
- An electric bulb has a filament connected to its terminals.
- An electric bulb glows when electric current passes through it.
- In a closed electric circuit, the electric current passes from one terminal of the electric cell to the other terminal.
- A switch is a simple device used to either break the electric circuit or complete it.
- Materials that allow electric current to pass through them are called conductors.
- Materials that do not allow electric current to pass through them are called insulators.
Keywords
| Serial No. | Keyword | Serial No. | Keyword |
|---|---|---|---|
| 1 | Bulb | 5 | Filament |
| 2 | Conductors | 6 | Insulators |
| 3 | Electric cell | 7 | Switch |
| 4 | Electric circuit | 8 | Terminal |
