Electric Current and Its Effects Class 7 Notes Science Chapter 10

Electric Circuit Diagram

An electric circuit is an unbroken path through which an electric current can flow. A circuit diagram is a drawing of an electrical circuit with standard symbols representing the various components of the circuit. Standard symbols are used for basic components of electric circuits. The circuit should have a source, wires without any gaps, and a switch which can have a discontinuity.

Connecting Cells to Make a Battery
By connecting cells together, the voltage output can be increased. Identical cells should be connected in such a way that the positive terminal of one cell is connected to the negative terminal of the next cell.

Cell Holder
A cell holder is a place where cells are to be placed in battery-operated devices. They are also available separately and can be used in electrical circuits as needed. A cell holder is an open box made of plastic with metal contacts designed to hold one or more cells. They have ' 'and'-' signs inscribed inside, where the positive and negative terminals of the cells fit in.

Effects of Electric Current

• Electric current can cause heating effect, magnetic effect, and chemical effect.
• Heating effect of electric current is used in electric heaters, electric irons, and electric toasters.
• Magnetic effect of electric current is used in electric motors and generators.
• Chemical effect of electric current is used in electroplating and electrolysis.

Electric Conductors and Insulators

• Materials that allow electric current to pass through them are called conductors.
• Metals are good conductors of electricity.
• Materials that do not allow electric current to pass through them are called insulators.
• Rubber, plastic, and glass are good insulators of electricity.

Heating Effect of Electric Current

When electric current passes through a filament in an incandescent bulb, it gets heated due to the heating effect of the electric current. This heating effect is also used in several electrical appliances such as toasters, irons, hairdryers, and ovens. The same effect can be used both as a disadvantage and an advantage.

• Electric Toaster
  An electric toaster is an appliance that uses the heating effect of electric current to toast bread slices. The toaster has a coil of wire that gets heated when an electric current passes through it. The bread slices are placed between the heated wire and get toasted.
• Electric Iron
  An electric iron is an appliance that uses the heating effect of electric current to iron clothes. The iron has a heating element that gets heated when an electric current passes through it. The heat is transferred to the soleplate, which is used to iron clothes.
• Hot Plate
  A hot plate is an appliance that uses the heating effect of electric current to heat food. The hot plate has a heating element that gets heated when an electric current passes through it. The heat is transferred to the cooking vessel, which is used to heat food.
• Electric Hairdryer
  An electric hairdryer is an appliance that uses the heating effect of electric current to dry hair. The hairdryer has a heating element that gets heated when an electric current passes through it. The hot air is blown through the nozzle, which is used to dry hair.
• Electric Oven
  An electric oven is an appliance that uses the heating effect of electric current to cook food. The oven has a heating element that gets heated when an electric current passes through it. The heat is transferred to the food, which is cooked inside the oven.
• Electric Fuse
  A safety device used in electric circuits to prevent damage to appliances from excessive current flow. Consists of a thin wire made of materials that melt easily when heated. Works on the principle of heating effect of current. When the current exceeds a certain maximum amount, the fuse wire melts and breaks the circuit.
• Miniature Circuit Breaker (MCB)
  An automatically operated electric switch that protects an electric circuit during overload or short circuit. Can be manually or automatically reset to restore normal operation. Found on the distribution board or switchboard of a house.
• Safety Measures During Electrical Fire
  Switch off the electric supply by switching off the mains. Identify the switch of the mains in your house and take the help of an adult while doing this.

Magnetic Effect of Electric Current

Activity to demonstrate the magnetic effect of current-carrying conductors
Electromagnet: a device that acts like a magnet when electric current is passed through it.
Increase in magnetic effect by making many turns of wire and wrapping it around a magnetic material.
Commercially used electromagnets have insulated wire wound tightly around a cylindrical core with soft iron for increased strength

Question for Chapter Notes: Electric Current & Its Effects

Try yourself:Which scientist discovered the magnetic effect of electric current?

• A.

  Michael Faraday
• B.

  James Clerk Maxwell
• C.

  Hans Christian Oersted
• D.

  Nikola Tesla

Explanation

Oersted discovered the magnetic effect of electric current in 1820 when he noticed that a compass needle near a wire carrying an electric current was deflected from its normal position. This discovery led to the development of electromagnetism and its applications in various fields.

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Solenoid: long wire wound many times in a tight coil around a hollow or solid core, often used as an electromagnet
Scientist Profile: Hans Christian Oersted

• Physicist and chemist born in Denmark in 1777
• Known for discovery of magnetic effect of electric current
• Demonstrated deflection of magnetic needle near current-carrying wire
• Unit of magnetic field strength in CGS system named cersted in his honour

Uses of Electromagnets

Electromagnets are used in many devices in our daily lives. Examples include cranes, loudspeakers, telephones, electric fans, and washing machines. Electromagnets are also used in electric bells to produce a ringing sound.

Question for Chapter Notes: Electric Current & Its Effects

Try yourself:Which of the following devices uses an electromagnet to produce sound?

• A.

  Electric Heater
• B.

  Electric Fan
• C.

  Electric Buzzer
• D.

  Electric Kettle

Explanation

An electric buzzer is a device that uses an electromagnet to produce sound. When an electric current flows through the electromagnet, it creates a magnetic field that attracts a metal armature. This armature then strikes a metal plate or diaphragm, producing a sound. Electric heaters, fans, and kettles do not use electromagnets to produce sound.

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• Electric Bell
  An electric bell has an electromagnet that pulls a strip of iron to hit a gong and produce a ringing sound. When the switch is on, the electromagnet attracts the iron strip, causing the hammer to hit the gong. This process repeats quickly to produce a continuous ringing sound.
• Electric Buzzer
  Electric buzzers are used in various places such as doorbells, alarms, and electronic games. They work on a different principle than electric bells. The switch of a buzzer also causes an electric current to flow, but instead of hitting a gong, it produces a buzzing sound.

Key Words

Activity 1:

Aim: To demonstrate the heating effect of electric current.
Materials needed: A nichrome wire, a battery, a switch, a voltmeter, an ammeter, a thermometer.
Method: Connect the nichrome wire to the battery through the switch, voltmeter, and ammeter. Measure the voltage and current passing through the wire. Switch on the current and measure the temperature of the wire using the thermometer.
Observation: The wire heats up due to the flow of electric current. The temperature of the wire increases as the current passing through it increases.
Conclusion: The heating effect of electric current can be demonstrated using a simple circuit. The amount of heat produced depends on the resistance of the wire and the amount of current passing through it.

Activity 2:

Aim: To demonstrate the magnetic effect of electric current.
Materials needed: A battery, a wire, and some nails.
Method:
1. Connect the wire to the battery.
2. Touch the ends of the wire to the nails.
Observation:
When the wire is connected to the battery, and the ends of the wire touch the nails, the nails become magnetic.
Conclusion:
This activity demonstrates the magnetic effect of electric current. When electric current flows through a wire, it produces a magnetic field that can magnetize nearby objects.