Page 1 :
Class- 7th, Subject- Science, Chapter 13 Electric current and its Effects, , F. Answer the following question on one word or a sentences, , 1. What is a circuit diagram?, Ans- Circuit diagram is the schematic representation of an electric, circuit using standard symbols for various components of a circuit., 2. Name an alloy used to make heating elements., Ans- Nichrome, , 3.Define an electromagnets, Ans- An electromagnet is a device that acts as a magnet when, electric current flows through its coil., 4. Name the material used to make the filament of an electric bulb, Ans- Tungsten, 5. Name an appliance that uses an electromagnet, Ans- Electric bell, G. Answer the following question in brief, 1.Explain why a bulb gets heated when current flows through it., Ans- The filament is made up of tungsten element (with very high, melting point) that gets heated when electric current passes through, it. Hence, the bulb gets heated as the current passes through it.
Page 2 :
2.Draw circuit diagram for open and closed circuits., Ans- Draw diagram from textbook page no. 182 fig no. 13.2, 3.Why is fuse wire made up of a material with low melting point?, Ans- Fuse wire is made up of a material with low melting point to, prevent electrical appliances from getting damaged due to excess, heat generated by large amounts of current. Its work on the, principle of heating effect of current., , 4. Explain heating effect of current. Name two devices that use this, effect for their working, Ans- When the electric current flows through a conductor, the, electric energy gets converted into heat energy. The heating effect of, electric current occurs because certain conducting materials resist, the passage of electric current through them, resulting in the, conversion of some electrical energy into heat energy. Two devices, that use this effect are electric iron and electric water heater., 5. Write any two factors on which the strength of the magnetic field, of a solenoid depends., Ans- The strength of the magnetic field of a current-carrying solenoid, depends on the amount of current flowing through it, the number of, turns of the coil and the material of the solenoid., 6. List three uses of electromagnets., Ans- Three uses of electromagnets:, • In large cranes to lift heavy metal objects in factories, • To separate metal scrap at recycling plants, • In electrical appliances such as televisions, radios, tape recorders,, speakers and headphones.
Page 3 :
H. Answer the following question in details, 1.Draw standard symbols for the following components of an electric, circuit., Ans- a. Dry cell b. Open electric switch c. Closed electric switch d., Electric fuse e. Electric bulb, Ans- Draw symbols from textbook page no. 183, 2.Why is a fuse used in circuit? How does it work?, Ans- A safety device used in an electric circuit to prevent it from, getting damaged due to excess current flowing through the circuit is, called a fuse. It prevents electrical appliances from getting damaged, due to excess heat generated by large amounts of currents. An, electric fuse works on the principle of the heating effects of electric, current. It consists of a short thin wire (fuse wire) made of a material, with a low melting point. The fuse wire melts easily when heated due, to excess current and breaks the circuit. No electric current can flow, through the broken circuit and thus, the fuse protects the circuit, from damage., 3.Describe a simple experiment to demonstrate the magnetic effect, of electric current., Ans- Aim: To demonstrate the magnetic effect of electric current, Materials required: A dry cell, insulated copper wires, an electric, switch and a magnetic compass, Procedure:, i., ii., iii., , Set up a circuit using the dry cell, copper wire and electric, switch on a table., Place the magnetic compass next to the insulated copper, wire. Note the position of the needle in the compass., Turn the switch ON. What changes do you observe in the, compass needle?
Page 4 :
Observation: When the switch is turned ON and electric current, flows through the circuit, the needle of the compass is deflected, from its original position. When the switch is turned OFF, the, needle swings and returns to its original position., Conclusion: The current flowing through the wire produces, magnetic field around it due to which the magnetic compass needle, shows deflection., , 4. What is electromagnet? Describe how a simple electromagnet is, made, Ans- An electromagnet is a device that acts as a magnet when, electric current flows through its coil. An electromagnet consists of a, magnetic material such as a piece of soft iron placed within a coil of, wire connected in a circuit. When an electric current is passed, through the circuit, the electromagnet acquires magnetic properties., , 5.Describe the construction and working of an electric bell, Ans- The circuit of an electric bell consists of an electromagnet, a, hammer-like soft iron bar fixed on a spring, a contact screw (S) and, an iron strip (P). When the circuit is completed, the electromagnet, exerts a magnetic effect. It attracts the soft iron bar and the hammer, strikes the gong. As the iron bar moves towards the electromagnet,, the iron strip (P) loses its contact with the screw (S). This stops the, current flowing through the circuit, and the electromagnet loses its, magnetic property. The hammer returns to its original position and, the contact screw once again completes the circuit. The hammer, then hits the going again, and this process continues as long as the, switch is kept on. This generates the ringing sound of the electric, bell.
