Friday, December 30, 2011

CBSE VII SCIENCE Electric Current and its effects NCERTSolutions

Q1 What is meant by electric current?
Ans-Electric Current : Flow of electrons.
Q2 What is an electrc circuit?
Ans -Electric Circuit : The closed path in which electric current flows.
Q3 Under what conditions a circuit is said to be complete?
Ans-Current can flow through a circuit only if it is complete i.e. all its parts are made up of a conductor.
Q4 What is a switch?
Ans -Switch is used to close and open a circuit. When switch is ‘ON’ circuit is complete and current flows through it and when it is ‘OFF’ circuit breaks (air is an insulator) and flow of current stops.
Q5 Draw the symbols for various Components of an electric circuit ?
Cell : Source of electric current. 
 Battery : Combination of 2 or more cells 
Connecting Wires – generally insulated Copper wires. 
Electric Bulb – Key or switch-Open key-Closed key
Note : When cells are connected to form a battery positive terminal of one is always connected to negative terminal of the other.
Q6 What is a circuit diagram?
Ans—In an electrical Circuit when we replace electrical components with their symbols we call it Circuit diagram.

Q7 What do mean by heating effect of current?
Ans--When current flows through a metal wire it gets heated up, this is called heating effect of current. e.g. a glowing electric bulb becomes warm.
Q8 Name few appliances which use heating effect of current.
Ans--Appliances using heating effect of current Electric Iron, room heater, electric heater, geyser, hair dryers etc.
Q10 What are filaments of a bulb and a heater made up of?
Ans--In a bulb there is a thin wire called the filament made up of tungsten. When current passes through it, it glows and gets heated up. In a heater there is a coil of wire called element which is made up of nichrome. When current passes through element it becomes red hot and give out heat.
Q11 What are the factors on which amount of heat produced depends?
The amount of heat produced in a wire depends on
(A) Its material – better conductors produce less heat; e.g. Elements of electric appliances are made of nichrome whereas connecting wires are made up of copper which is a better conductor so they do not get heated up as the element.
(B) Its length – as length increases heat produced increases; e.g. elements are coiled in heaters to increase length.
(C) Thickness – as thickness increases heat produced decreases; e.g. lead wires of iron, heater etc. are thicker than normal connecting wire so that they don’t get heated up easily.
Q12 What is an electric fuse?
Ans---Electric Fuse - A Safety device in domestic circuit used to prevent electrical fire due to short circuit or overloading.
Q 13.Name any two effects of electric current.
Ans : Heating Effect : When an electric current flows through a wire, the wire gets heated. It is the heating effect of current due to resistance of wire that flow of current. This effect has many applications like Electric Heater, Light Bulb etc.
Magnetic effect : When an electric current flows through a wire, it produces magnetic effect around it that is detected by magnetic compass. Magnetic Effect of electric current use in Electric Bell, Motor, Fan etc.
Q 14.Fill in the blanks:
(a) Longer line in the symbol for a cell represents its ------- terminal.
(b) The combination of two or more cells is called a -------- .
(c) When current is switched ‘on’ in a room heater, it ----------.
(d) The safety device based on the heating effect of electric current is called a -------.
Ans: (a)negative (b) battery(c) gives out heat (d)fuse
Q 15. Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell.
(b) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks.
(c) An electromagnet does not attract a piece of iron.
(d) An electric bell has an electromagnet. 
(a)     (F)         (b) (T)              (c)(F)              (d)(T) 

No comments:

Post a Comment