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Symbols of Electric Components
Fun with Circuits
- Game Time: Remember the game “How steady is your hand?” from Class VI? Paheli and Boojho had lots of fun playing it with their family and friends.
- Drawing a Circuit: Paheli drew a circuit to explain the game to a cousin.
Symbols of Electric Components
- Why Symbols?: Boojho wondered if there’s an easier way to represent electric components.
- Common Symbols: Some electric components have standard symbols. Check Table 10.1 for details.
- Electric Cell Symbol:
- Long Line: Positive terminal.
- Short Thick Line: Negative terminal.
- Switch Symbol: Different symbols for ‘ON’ and ‘OFF’ positions.
- Wires: Represented by simple lines.
What is a Battery?
- Battery Symbol: Shown in Table 10.1.
- Making a Battery: Connect two or more cells. Positive terminal of one cell connects to the negative terminal of the next (Fig.10.2).
Using Batteries in Devices
- Devices: Torches, toys, TV remotes, etc.
- Cell Placement: Sometimes cells are side by side, connected by a metal strip inside the device (Fig.10.3).
- Cell Holder: You can make one or buy from the market. Ensure proper connections (Fig.10.4 and Fig.10.5).
Drawing Circuit Diagrams
Activity 10.1: (click here)
Make an electric circuit (Fig.10.7) and draw it using symbols.
- Circuit Diagram: Easier to draw using symbols (Fig.10.8).
- Comparison: Compare your diagram with Fig.10.8 and Fig.10.9.
How Does a Bulb Work?
- Bulb Glows: Only when the switch is ‘ON’ and the circuit is closed.
- Filament: A thin wire inside the bulb that glows when electric current passes through it.
- Fused Bulb: If the filament is broken, the circuit is incomplete, and the bulb won’t glow.
Important Points
- Switch Position:
- ‘ON’ Position: Circuit is complete (closed), and current flows.
- ‘OFF’ Position: Circuit is incomplete (open), and no current flows.
Heating Effect of Electric Current
Activities to Understand Heating Effect
Activity 10.2
- Materials: Electric cell, bulb, switch, and wires.
- Steps:
- Make a circuit (Fig.10.9) with the switch in ‘OFF’ position.
- Touch the bulb.
- Switch to ‘ON’ position, let the bulb glow for a minute.
- Touch the bulb again.
- Switch back to ‘OFF’ and touch the bulb.
- Observation: The bulb gets warm when it glows.
Activity 10.3
- Materials: Circuit (Fig.10.10), 10 cm nichrome wire.
- Steps:
- Tie nichrome wire between nails.
- Switch ‘ON’ and touch the wire after a few seconds.
- Switch ‘OFF’ and touch the wire again after a few minutes.
- Observation: The wire gets hot when current passes through it.
Heating Effect in Daily Life
- Appliances: Room heaters, cooking heaters, irons, geysers, electric kettles, hair dryers.
- How it Works: These devices have a coil of wire (element) that becomes red hot and gives off heat when current flows through it.
- Factors Affecting Heat: Material, length, and thickness of the wire.
Safety and Efficiency
- Wire Melting: If too much current flows, wires can melt and break.
- Electric Fuses:
- Purpose: Prevent overheating and fires by breaking the circuit when current exceeds safe limits.
- Usage: Found in buildings and electrical appliances.
- Materials: Special wires that melt quickly with large currents.
Activity 10.4
- Materials: Circuit from Activity 10.3, four-cell battery, thin steel wool strand.
- Steps:
- Replace cell with battery and nichrome wire with steel wool.
- Pass current and observe if the wool melts and breaks.
- Observation: Steel wool melts and breaks with high current.
Advanced Safety Devices
- Miniature Circuit Breakers (MCBs):
- Function: Automatically turn off when current exceeds safe limits.
- Benefit: Can be reset by turning them on again.
- ISI Mark: Look for this mark on electrical products for safety and quality assurance.
Energy Efficient Lighting
- Incandescent Bulbs: Waste a lot of energy as heat.
- Better Options: Fluorescent tube-lights, CFLs, and LEDs.
- LEDs: Most efficient, consume less electricity, and provide the same light intensity.
- Safety Note: Fluorescent tubes and CFLs contain toxic mercury and should be disposed of safely.
Important Points
- Short Circuits: Caused by direct touching of wires due to damaged insulation.
- Overloading: Connecting too many devices to one socket can cause excessive current flow.
Caution
- Proper Fuses: Always use the correct fuse for the application with an ISI mark. Do not replace fuses with random wires or metal strips.
Magnetic Effect of Electric Current
Activity 10.5: Observing Magnetic Effects
- Materials: Cardboard tray from a matchbox, electric wire, small compass needle, electric cell, switch.
- Steps:
- Wrap the wire around the cardboard tray.
- Place the compass inside and connect the wire ends to a cell through a switch (Fig.10.17).
- Note compass needle direction.
- Bring a bar magnet near the compass.
- Switch ‘ON’ the current and observe the needle.
- Switch ‘OFF’ the current and observe again.
- Observation: The compass needle deflects when the current flows, showing the wire behaves like a magnet.
- Conclusion: Electric current makes a wire act like a magnet (Magnetic Effect of Electric Current).
Concept: Electric current makes a wire act like a magnet (Magnetic Effect of Electric Current).
Electromagnet
- Making an Electromagnet:
- Materials: 75 cm insulated wire, 6-10 cm iron nail, electric cell, switch.
- Steps:
- Wind the wire tightly around the nail forming a coil (Fig.10.19).
- Connect the wire ends to the cell through the switch.
- Place pins near the nail and switch ‘ON’ the current.
- Observation: Pins cling to the nail when the current flows.
- Conclusion: The coil behaves like a magnet when current flows. This is an electromagnet.
Uses of Electromagnets
- Strong Electromagnets: Can lift heavy loads (e.g., cranes).
- Separating Materials: Used to separate magnetic material from junk.
- Medical Uses: Doctors use tiny electromagnets to remove magnetic materials from the eye.
- Toys: Many toys have electromagnets inside them.
Electric Bell
- Components: Coil of wire (electromagnet), iron strip with hammer, contact screw.
- How It Works (Fig. 10.20):
- When the iron strip contacts the screw, current flows through the coil, making it an electromagnet.
- The electromagnet pulls the iron strip, making the hammer strike the gong.
- This breaks the circuit, stopping the current and demagnetizing the coil.
- The iron strip returns to its original position, completing the circuit again.
- This process repeats rapidly, making the bell ring.
Summary
- Magnetic Effect of Electric Current: When current flows through a wire, it behaves like a magnet.
- Electromagnets: Coils of wire that become magnetic when current flows through them.
- Electric Bell: Uses an electromagnet to make the hammer strike the gong, producing sound.
Chapter Summary:
- It is convenient to represent electric components by symbols.
- Using these symbols, an electric circuit can be represented by a circuit diagram.
- When an electric current flows through a wire, the wire gets heated.
- This is the heating effect of current.
- This effect has many applications.
- Wires made from some special materials melt quickly and break when large electric currents pass through them.
- These materials are used for making electric fuses.
- Electric fuses prevent fires and damage to electric appliances.
- When an electric current flows through a wire, it behaves like a magnet.
- A current-carrying coil of an insulated wire wrapped around a piece of iron is called an electromagnet.
- Electromagnets are used in many devices.
Keywords
| Serial No. | Keywords | Serial No. | Keywords |
|---|---|---|---|
| 1 | Battery | 5 | Electromagnet |
| 2 | Circuit diagram | 6 | Fuse |
| 3 | Electric components | 7 | Heating effect of current |
| 4 | Electric bell | 8 | Magnetic effect of current |
