CG Board Class 7 Science Electric Current and Its Effect
Electric Components and Symbols:
- Electric components like cells, batteries, switches, and wires can be represented by symbols in circuit diagrams.
- An electric cell has a positive terminal (represented by a longer line) and a negative terminal (represented by a thicker, shorter line).
- Cells are connected in series to form batteries, which are used in various devices.
- Switches have symbols to represent their ‘ON’ and ‘OFF’ positions.
- Wires are represented by lines connecting components in circuit diagrams.
Conductors and Insulators:
- Conductors allow electric current to pass through them and include metals, alloys, graphite, and electrolytes.
- Insulators do not allow electric current to flow through them and include non-metals (except graphite), wood, glass, plastic, dry air, and most gases.
- Conductors are used in electrical plugs, sockets, and switches, while insulators are used to cover electrical wires and prevent electric current from escaping.
Effects of Electric Current:
- When an electric current passes through a conductor, it exhibits three main effects: heating, magnetic, and chemical.
- The heating effect is due to the resistance offered by the conductor, which converts part of the electrical energy into heat. This principle is used in devices like electric bulbs, heaters, and soldering irons.
Safety Devices – Fuses:
- Fuses are safety devices used to prevent electrical circuit damage and potential fires.
- Fuses are made of materials like zinc or alloys of lead and tin with low melting points.
- If the current in a circuit exceeds a safe limit, the fuse wire melts and breaks the circuit, preventing accidents.
Magnetic Effect of Electric Current:
- When electric current flows through a wire, it generates a magnetic field.
- Electromagnets are created by coiling a wire and are used in various applications, including electric bells, telephones, loudspeakers, cranes, and electric motors.
Electric Bell and Its Function:
- An electric bell functions based on the magnetic effect of electric current.
- It contains an electromagnet that attracts an iron armature when current flows through it, causing a hammer to strike a metallic cap, producing sound.
- A push button is often used to activate electric bells, and they continue to ring as long as the button is pressed.
Electrical Safety Precautions:
- Electrical accidents, such as electric shocks, can be dangerous, even fatal.
- Precautions include securely screwing switches, plugs, and connections, covering exposed wires with insulating tape, using properly sized fuse wires, ensuring grounding in electrical devices, wearing protective gear during repairs, and cutting off the main switch in emergencies.
- In case of an electric shock, use insulating materials like dry wood, rubber, or plastic to remove the person from the circuit to prevent further injuries.
Choose the correct alternative:
- The materials which allow electric current to pass through them are called-
- (a) Conductor
- (b) Insulators
- (c) Semi conductor
- (d) Sometimes conductor, Sometimes insulator
- The following is not a good conductor of electricity –
- (a) Copper
- (b) Brass
- (c) Graphite
- (d) Glass.
- Filament of electric bulb is made up of –
- (a) Nichrome
- (b) Tungsten
- (c) Chromium
- (d) Tin
- Electric heater shows following effect of electric current –
- (a) Heating effect
- (b) Magnetic effect
- (c) Chemical effect
- (d) All of these
Which appliance is made on the basis of magnetic effect of electric current –
- (a) Electric bulb
- (b) Electric bell
- (c) Electric iron
- (d) Soldering iron
Fill in the blanks –
- In the symbol of electric cell, the longer line represents the ——- terminal.
- Combination of two or more electric cells is called ————–.
- Electric bulb shows —————— effect of electric current.
- In loudspeakers —————— effect of electric current is used.
- Melting point of fuse wire is very ————–.
- In the symbol of electric cell, the longer line represents the positive terminal.
- Combination of two or more electric cells is called a battery.
- Electric bulb shows the heating effect of electric current.
- In loudspeakers, the magnetic effect of electric current is used.
- The melting point of fuse wire is very low.
Answer the following questions –
- What are the important components necessary for an electric circuit?
Important Components for an Electric Circuit:
Electric source , Conductors ,Switches,Loads ,Safety devices,Insulators .
- Explain the heating effect of electric current.
The heating effect of electric current is the phenomenon where electrical energy is converted into heat when current passes through a conductor. This occurs due to the resistance offered by the conductor. The resistance results in the generation of heat, causing the conductor to become hot. This principle is applied in devices like electric bulbs, heaters, and soldering irons.
- Write two uses of magnetic effect of electric current.
Electric Bells: Electric bells use the magnetic effect of electric current to attract an iron armature when the circuit is closed, causing the bell to ring.
Loudspeakers: Loudspeakers use the interaction of current with magnets to produce sound waves.
- Write three uses of an electromagnet.
Uses of Electromagnet:
- Electric Cranes: Electromagnets are used in cranes to lift heavy objects.
- Scrap Yards: Electromagnets are employed to separate iron from garbage in scrap yards.
- Electrical Devices: Electromagnets are used in various electrical devices such as electric motors, generators, and electric trains.
