Long Answer -Class 10 -Science- Physics-Chapter 12:Electricity

Class 10 -Science-Long Answer – Physics-Chapter 12:Electricity

Q1. a.What is meant by saying that the potential difference between two points is 1 volt?

b. Why does the connecting cord of an electrical heater not glow while the heating element does?

c. Electrical resistivity of some substance at 20°C are given below:

Material	Resistivity (ρ) (Ω·m)
Silver	1.60×10−81.60×10−8
Copper	1.62×10−81.62×10−8
Tungsten	5.21×10−85.21×10−8
Iron	1.00×10−71.00×10−7
Mercury	9.40×1069.40×106
Nichrome	1.00×10−61.00×10−6

Answer the following questions in relation to them:

i. Among silver and copper which one is better conductor? Why?

ii. Which material would you advise to use in electrical heating device? Why?

Ans :

a. If the amount of work done in bringing a unit positive charge from one point to another is 1 J in an electric field then potential difference b/w the two points is said to be 1 volt. 1V = 1C/ 1 J

b. Connected cord of an electrical heater does not glow because this is of copper metal, which has low resistivity and good conductivity. Heating element glows due to its high resistivity or poor conductivity.

c. (i) The resistivity of silver is lesser than copper so it is a good conductor.

(ii) The resistivity of nichrome is maximum in the given table so nichrome will be advised to use in electrical heating device.

Q2. What is meant by resistance of a conductor? Name and define its SI unit. List the factors on which the resistance of a conductor depends. How is the resistance of a wire affected if:

a. its length is doubled,

b. its radius is doubled?

Ans : Property of any conductor by virtue of which it opposes the flow of current in the conductor is called its resistance.

SI unit of resistance is Ohm. If by applying a potential difference of 1 volt the current in the conductor is 1 A. Then the resistance of the conductor is said to be 1 ohm.

Factor affecting resistances:

a. If length is double then resistance also becomes doubled.

b. If radius is doubled then area A = π( 2r)² becomes 4 times, then the resistance becomes 1/4.

Q4. Draw a circuit diagram for a circuit consisting of a battery of five cells of 2 volts each, a 5Ω resistor, a 10 Ω resistor and a 15 Ω resistor, an ammeter and a plug key; all connected in series. Also, connect a voltmeter to record the potential difference across the 15 Ω resistor and calculate: a. the electric current passing through the above circuit and b. potential difference across 5 W resistor when the key is closed.

Ans:

If by applying a potential difference of 1 volt across a conductor, the current is 1A then the resistance of the conductor is said to be 1 ohm. Two disadvantages of connecting electrical appliance in series.

a. If one appliance fails to operate then the circuit is broken and other devices also will not operate.

b. Different devices require different amount of current to operate but in series combination, same current is supplied to all electrical appliances.