NCERT Science Class 10 Chapter 16 Electricity CBSE Board Sample Problems Very Short Answer
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Question
Why is tungsten metal used in bulbs but not in fuse wires?
Solution
ANS-It is because tungsten has a very high melting point.
If it is used as a fuse wire, then it will not melt even when large amount of current is passed through it, and the appliance will be damaged
Question
Why are copper wires used as connecting wires?
Solution
The electrical resistivity of copper is low.
Question
(1)By what other name is the unit joule/coulomb called?
Solution
Volt
Question
Nichrome is used to make the element of an electric heater why?
Solution
Nichrome is an alloy of high resistivity and high melting point and does not oxidise easily
Question
Name the instrument used to measure
(i) Electric current in a circuit,
(ii) Potential difference between two points in a circuit
Solution
(i) Ammeter,
(ii) Voltmeter
Question
State Ohm’s Law
Solution
According to Ohm’s Law at constant temperature and pressure, the current passing through a conductor is directly proportional to the potential difference across its end, i.e.
Question
When do we say that the potential difference between two points of a circuit in 1 voIt
Solution
Potential difference between two points of an electric circuit is said to be 1 volt when a work of 1 J is to be done for moving a charge of 1 C between two points.
Question
What happens to the resistance of a conductor when temperature is increased?
Solution
The resistance of a conductor increase with rise in temperature. As R ci T.
Question
Why is tungsten used for making filament of electrical bulbs?
Solution
Because tungsten has high melting point and high (resistivity).
Question
Why do we prefer using copper and aluminium for transmission of electric current?
Solution
Because of their low resistivity /cost.
Question
Two bulbs having power of 50 w and 25 w respectively are connected with the same source. Which has higher resistance?
What is their ratio?
Solution
¡e, 50 W bulb has ½ resistance than 25 W.
Question
A wire of resistance 5 is bent in the form of a closed circle.
Find the resistance across the diameter of the circle?
Solution
R=5
Consider two semicircular elements connected across the diameter.
Total resistance is 5
Resistance of two semicircular elements is
Both the elements are connected in parallel.
Question
List any two factors on which resistance of a wire depends on.
Solution
Resistance depends on:
Length of wire (directly proportional)
Cross-sectional area (inversely proportional)
Question
The electric power consumed by a device may be calculated by either of the two expressions or . the first expression indicates that it is directly proportional to R whereas the second expression indicates inverse proportionality. How can the seemingly different dependence of P on R in these expressions be explained? (1)
Solution
is used to calculate electric power when the current flowing through the circuit is constant (Series combination).
(1/2)
is used to calculate electric power when the potential difference flowing through the circuit is constant (Parallel combination). (1/2)