Chhattisgarh State Board Class 7 Science Chapter 21 Electric Current and Its Effect Exercise MCQ, True or False, Questions and Answers here.
(1) Choose the correct alternative:
(1) The material which allow electric current to pass through them are called –
(a) Conductor
(b) Insulators
(c) Semi conductor
(d) Sometimes conductor, sometimes insulators
Answer:- (a) Conductor.
(2) Following is not a good conductor of electricity –
(a) Copper
(b) Brass
(c) Graphite
(d) Glass
Answer:- (d) Glass.
(3) Filament of electric bulb is made up of –
(a) Nichrome
(b) Tungsten
(c) Chromium
(d) Tin
Answer:- (b) Tungsten.
(4) Electric heater shows following effect of electric current –
(a) Heating effect
(b) Magnetic effect
(c) Chemical effect
(d) All of these
Answer:- (d) All of these.
(5) 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
Answer:- (b) Electric bell.
(2) Fill in the blanks –
(1) In the symbol of electric cell, the longer line represents the ——-.
Answer:- Positive terminal.
(2) Combination of two or more electric cells is called ——-.
Answer:- battery.
(3) Electric bulbs shows —— effect of electric current.
Answer:- Heating.
(4) In loudspeakers —— effect of electric current is use.
Answer:- Magnetic.
(5) Melting point of fuse wire is very —–.
Answer:- Low.
(3) Answer the following questions –
(1) What are the important component necessary for an electric bulb.
= The important components necessary for an electric circuit are –
(1) The source of electricity i.e. – cell/battery
(2) The device which needs electrical energy i.e. – bulb
(3) Connecting wires which are made of conducting material such as copper.
(4) A key or switch by the circuit which can be opened and closed
(2) Explain the heating effect of electric current.
Answer:- The heating effect of electric current
(1) Whenever current passes through a material then part of its energy is converted into heat energy and the material get heated.
(2) This is due to the resistance offered by the conductor to the flow of current.
(3) This is a quality of a conductor to resist the flow of current.
(3) Write uses of magnetic effect of electric current.
Answer:- Uses of magnetic effect of electric current as follows:-
(1) The magnetic effect of electric current is used in making electromagnets.
(2) Electric bell is a device which is based on the magnetic effect of electric current.
(4) Write three uses of an electromagnet
Answer:- Uses of an electromagnet are –
(1) In electric bells, telephones, telegraph and in loudspeakers.
(2) In cranes, to lift heavy objects.
(3) To separate iron from garbage.
(4) In electric motors, electric trains, electric generator etc.
(5) Write the working method of an electric bell with the help of a labeled diagram.
Answer:- The working of an electric bell fig shows The circuit of an electric bell.
(1) In this ‘M’ is a electromagnet in which two end of the coil are attached to screws ‘P’ and ‘Q’ which are in turn attached to the electric source – the cell.
(2) When electric current passes through the coil, the electromagnet become magnetic and attracts the thin iron sheet armature ‘a’ toward itself.
(3) This armature is attached to a spring ‘C’ in its normal state this spring it attached to the armature ‘A’. The other and of armature is attached to a hammer ‘H’ & ‘B’ is a metallic cap or bowl.
(4) When the battery is joined to P and Q, the electromagnets attracts armature A which makes the hammer strike the bowl ‘B’ and makes a sound.
(5) When this process is repeated the electric bell rings.
(6) Write important methods from preventing electric shocks.
Answer:- Important methods from preventing electric shocks are –
(1) All the switches, plugs, and connection in an electric circuit must be tightly screwed or fixed.
(2) All the electrical gadgets such as, refrigerator, heater and washing machines must have earthling.
(3) If there is a fire or any other accidents the key of the electric current must be cut off or the switch must be put off.