Definitions [3]
Definition: Fuse
An electric fuse is a safety device which is used to limit the current in an electric circuit. The use of a fuse safeguards the circuit and the appliances connected in that circuit from being damaged.
Definition: Switch
A switch is an on-off device for current in a circuit (or in an appliance). It is connected in the live wire.
Definition: Socket
It is a fixture in an electric circuit in which the plug is inserted.
Formulae [1]
Formula: Current Rating of Fuse
Current Rating of Fuse in a Circuit = \[\frac{\text{total power of appliances in circuit}}{\text{voltage of the supply}}\]
Key Points
Key Points: Transmission of Electric Power
- Electric power is generated at 11 kV and transmitted at very high voltage because high voltage results in low current and hence less energy loss due to heating in transmission lines.
- Alternating current (50 Hz) is used since its voltage can be stepped up and stepped down using transformers, which is not possible with d.c.
- The voltage is stepped down in stages from 132 kV → 33 kV → 11 kV → 220 V before supplying electricity to domestic consumers.
Key Points: Power Distribution to a House
- Electric supply to a house is provided through three wires—live (L), neutral (N), and earth (E) —with the neutral and earth wires at the same potential (0 V).
- The company fuse and main fuse (or MCB) are connected to the live wire, while the main switch (or ELCB) is connected to both the live and neutral cables for safety.
Key Points: Three-Core Flexible Cable
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Each electric appliance is provided with a three-core flexible cable consisting of live, neutral, and earth wires.
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The colour coding of the wires is fixed: red (or brown) for live, black (or light blue) for neutral, and green for earth wire.
Key Points: High Tension Wires
- High-tension wires have low resistance, allowing heavy current to pass with minimal heating.
- High-tension wires are made by twisting many thin, insulated wires together, which provides a large surface area for rapid heat dissipation.
Important Questions [20]
- In the transmission of power the voltage of power generated at the generating stations is stepped up from 11kV to 132 kV before it is transmitted. Why?
- Name the device used to increase the voltage at a generating station.
- Which electrical component protects the electric circuit in case of excess current and which can also be used as a switch?
- Name the wire to which this electrical component is connected in an electric circuit.
- Identify the Following Wires Used in a Household Circuit: The Wire is Also Called as the Phase Wire.
- For a Fuse, Higher the Current Rating ________ is the Fuse Wire.
- (I) Write One Advantage of Connecting Electrical Appliances in Parallel Combination. (Ii) What Characteristics Should a Fuse Wire Have ?
- State the Characteristics Required in a Material to Be Used as an Effective Fuse Wire.
- Identify the option that displays the correct wiring with correct colour code:
- To Which Wire Should the Fuse Be Connected?
- Explain the Meaning of the Student ‘Current Rating of a Fuse is 5a’.
- A Fuse is Rated 8a. Can It Be Used with an Electrical Appliance Rated 5 Kw, 200 V ? Give a Reason.
- Name the Wire in a Household Electrical Circuit to Which the Switch is Connected
- The Diagram Below Shows a Dual Control Switch Circuit Connected to a Bulb. (I) Copy the Diagram and Complete It So that the Bulb is Switched On.
- Draw the diagram of a dual control switch when the appliance is switched ‘ON’.
- An Electric Iron is Rated 220v, 2kw. If the Iron is Used for 2h Daily Find the Cost of Running It for One Week If It Costs 4.25 per Kwh and Why is the Fuse Absolutely Necessary in a Power Circuit?
- To Which Wire of a Cable in a Power Circuit Should the Metal Case of Geyser Be Connected.
- Identify the Following Wires Used in a Household Circuit: The Wire is Connected to the Top Terminal of a Three Pin Socket.
- Name the Color Code of the Wire Which is Connected to the Metallic Body of an Appliance.
- At what voltage is this current available to our household?
Concepts [13]
- Transmission of Power from the Power Generating Station to the Consumer
- Power Distribution to a House
- House Wiring (Ring System)
- Fuse
- Reason for connecting the fuse in the live wire
- Current Rating of a Fuse
- Switches
- Circuits with Dual Control Switches (Staircase Wire)
- Earthing
- Three-pin Plug and Socket
- Colour Coding of Wires in a Cable
- High Tension Wires
- Precautions to Be Taken While Using Electricity
