NCERT Solutions for Class 7th Science Chapter 10 Electric Current and Circuit according to the Latest Syllabus Of JKBOSE and CBSE Books
A. Fill in the blanks:
1. A drawing of an electrical circuit with standard symbols is called a/an ____________ (Circuit diagram/ electric diagram).
2. Hot plates, electric toasters, and electric irons get hot when switched on because of the ___________ effect of current. (Magnetic/heating)
3. A fuse is a __________ device. (Safety/heating)
4. A wire twisted in the form of a circle is called a/an __________ (coil/electromagnet).
5. An __________ consists of a soft iron core with an insulated wire wound around it. (Electromagnet/electric magnet)
B. Choose the correct answer:
1. A circuit diagram is
(a) a picture of a circuit
(b) a drawing of a circuit with standard pictures for the different electrical components.
(c) a diagram of an electrical circuit with standard symbols for the different electrical components.
(d) a different representation of an electrical circuit.
Correct: (c) a diagram of an electrical circuit with standard symbols for the different electrical components.
2. When an electric current passes through a wire, the wire gets hot. This is called
(a) Joule heating
(b) conduction
(c) electricity
(d) thermal heating
Correct: (a) Joule heating
3. An electric fuse is
(a) a safety device
(b) an appliance
(c) used to produce electric current
(d) used to heat a room
Correct: (a) a safety device
4. When we bring a magnetic compass near a current-carrying wire,
(a) it deflects the magnetic needle of the compass
(b) it makes the magnetic needle point North
(c) it makes the magnetic needle point South
(d) it has no effect on the magnetic needle
Correct: (a) it deflects the magnetic needle of the compass
5. A coil refers to
(a) an electrical wire
(b) a fuse
(c) a current-carrying conductor
(d) a wire twisted in the form of a circle
Correct: (d) a wire twisted in the form of a circle
6. An electromagnet acts like a magnet
(a) when a current is passed through the coil
(b) all the time
(c) because it has a magnetic core
(d) only if a current does not pass through the coil
Correct: (a) when a current is passed through the coil
7. In an electric bell, we have
(a) an electromagnet
(b) a hammer
(c) an interrupter
(d) all of these
Correct: (d) all of these
8. In an electric bell, which of these gets attracted to the electromagnet?
(a) the hammer
(b) the gong
(c) the soft iron strip
(d) the screw
Correct: (c) the soft iron strip
9. Which of these does not use heating effect of current?
(a) electric toaster
(b) electric fan
(c) electric iron
(d) room heater
Correct: (b) electric fan
10. An electric fuse wire melts if the amount of current flowing through it
(a) more than a minimum amount
(b) less than a minimum amount
(c) more than a maximum amount
(d) less than a maximum amount
Correct: (c) more than a maximum amount
C. Answer the following questions:
1. What is an electrical circuit?
An electrical circuit is a path or network through which electric current flows. It consists of electrical components like resistors, capacitors, inductors, and power sources (battery or generator).
2. Draw an electrical circuit with an electrical cell, a bulb, and an ‘ON’ switch.
(This would be a simple drawing with a cell connected to a bulb and a switch in series.)
3. Why does an electric bulb get hot if it is kept ‘ON’ for a little while?
An electric bulb gets hot when it is kept ‘ON’ for a while due to the heating effect of electric current. The filament inside the bulb resists the electric current, causing it to heat up and glow.
4. Name three appliances that use the heating effect of electric current.
1. Electric iron
2. Electric toaster
3. Electric heater
5. What is an electric fuse?
An electric fuse is a safety device used to protect electrical circuits from overcurrent. It contains a thin wire that melts and breaks the circuit when the current exceeds a certain level, preventing damage to appliances and reducing the risk of fire.
6. Draw an electric fuse and explain briefly how it works.
(A simple drawing of an electric fuse would show a thin wire enclosed in a casing.) An electric fuse works by melting its internal wire when excessive current flows through it, thereby interrupting the circuit and stopping the flow of electricity.
7. How can you show that an electric current has a magnetic effect?
You can show that an electric current has a magnetic effect by using a magnetic compass near a current-carrying wire. When the current flows through the wire, the compass needle will deflect, indicating the presence of a magnetic field around the wire.
8. What is an electromagnet?
An electromagnet is a type of magnet whose magnetic field is produced by the flow of electric current. It consists of a coil of wire wrapped around a soft iron core. When current passes through the coil, it magnetizes the core, creating a strong magnetic field.
9. Name two factors on which the strength of an electromagnet depends.
1. The amount of electric current passing through the coil.
2. The number of turns in the coil of the electromagnet.
10. Explain the working of an electric bell using diagrams.
(A diagram of an electric bell would show an electromagnet, a hammer, a gong, and a contact screw.) When the switch is pressed, current flows through the electromagnet, creating a magnetic field that attracts the hammer. The hammer strikes the gong, producing sound. As the hammer moves, it breaks the circuit at the contact screw, causing the electromagnet to lose its magnetism and the hammer to return to its original position, ready to repeat the process.
