Textbook Solutions: Electric Current and Its Effects | Class 7 Oxford Science: Chapter Notes, Worksheets & Tests PDF Download

A. Choose the correct option.

1.
Ans: (c)

2.
Ans: (c)

3.
Ans: (b)

4.
Ans: (c)

B. Fill in the blanks with the correct words.

1.
Ans: The standard method for drawing electric circuits is called circuit diagrams.

2.
Ans: A fuse is a safety device that limits the amount of current in an electric circuit.

3.
Ans: An electromagnet acts like a magnet only when an electric current is on.

4.
Ans: Electric iron is based on the heating effect of electric current.

5.
Ans: An electric electromagnet is based on the magnetic effect of electric current.

C. Give reasons for the following.

1.
Ans: It is important to have standard methods of drawing circuit diagrams to ensure everyone can read and understand them easily. This helps to avoid misreading the diagrams, which can lead to serious and dangerous consequences.

2.
Ans: Sometimes filaments in an electric bulb get fused due to overheating caused by too much electric current flowing through them. The filament is a thin wire that heats up to produce light, and when the current is too high, it can overheat and melt or break, causing the bulb to "fuse" or burn out.

3.
Ans: Electric fuse wire is made of a material with a low melting point so that it melts and breaks the circuit if too much current flows through it. This is a safety feature designed to prevent damage to electrical appliances and possible fire hazards.

4.
Ans: A metal safety pin stuck to an electromagnet falls down when the current in the electromagnet is switched off because the magnetic field disappears when the current is switched off. This means that the electromagnet no longer has the ability to hold the pin, so it falls down.

D. Answer the following questions.

1.
Ans: Define/explain the following terms
(a) Electric circuit: An electric circuit is an unbroken path through which an electric current can pass. It consists of a source of electric current, conducting wires without any discontinuity and optional components like electric bulbs, switches, and electric appliances.
(b) Electric circuit diagram: An electric circuit diagram is a visual representation of an electric circuit where the components of the circuit are represented by standard symbols. It helps in understanding the functioning and arrangement of an electric circuit.
(c) Heating element: A heating element is a tightly wound coil found in electric appliances that produce heat like toasters, hot plates, electric irons, etc. It is designed to heat up when an electric current passes through it.
(d) Electric fuse: An electric fuse is a safety device used in electric circuits to prevent damage from unusually large amounts of current. It cuts off the supply of electric current when the current exceeds a certain limit.
(e) Electromagnet: An electromagnet is a piece of soft iron with an insulated wire wound around it that acts like a magnet when an electric current flows through it. Its magnetic strength depends on the number of turns of the wire and the amount of current flowing through the wire.

2.
Ans: The heating effect of electric current refers to the phenomenon where an electric current passing through a conductor or a circuit component causes it to heat up.

3.

Ans: Two appliances that use the heating effect of electric current are toasters and electric irons.

4.
Ans: An electric fuse is a safety device used in electric circuits to prevent damage from unusually large amounts of current. It contains a thin wire that allows a specific amount of electric current to pass through it. If the current exceeds this limit, the heat generated melts the wire and breaks the circuit, thus preventing potential damage or fire.

5.
Ans: An electromagnet is a piece of soft iron with an insulated wire wound around it that acts like a magnet when an electric current flows through it. Its properties include acting like a magnet only when current flows through the wire, losing its magnetic properties when the current stops, and having a magnetic strength that depends on the number of turns of the wire wound around its core and the amount of electric current flowing in the wire.

6.
Ans: Two uses of electromagnets are in electrical appliances with moving parts such as toasters, washing machines, fans, and mixer grinders, and in MRI machines used in hospitals and medical diagnostic centres.

7.
Ans: 
In an electric bell:
(a) Switch: The switch is used to start or stop the flow of electric current in the circuit.
(b) Electromagnet: The electromagnet pulls the soft-iron strip when the current flows, causing the hammer to hit the gong and produce sound.
(c) Soft-iron strip: The soft-iron strip is attracted to the electromagnet when the current flows, causing it to move and make the hammer hit the gong.
(d) Hammer and gong: The hammer hits the gong to produce sound when the soft-iron strip is attracted to the electromagnet.

8.
Ans: You can show that a current carrying wire produces a magnetic field by performing an experiment where you place a compass near a wire carrying electric current. The needle of the compass will deflect, indicating the presence of a magnetic field.