CBSE Class 10 Science Electricity Assignment Set D

Voltmeter: An apparatus to measure the potential difference or electric potential difference between two points in an electric circuit.
Galvanometer: It is a device to detect current in an electric circuit.
Ammeter: An apparatus to measure electric current in a circuit.

Multiple Choice Questions

Question: A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R’, then the ratio R/R’ is:
(a) 125
(b) 15
(c) 5
(d) 25

Answer: D

Question: Which of the following terms does not represent electrical power in a circuit?
(a) I2R
(b) IR2
(c) VI
(d) V2/ R

Answer: B

Question: An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be:
(a) 100 W
(b) 75 W
(c) 50 W
(d) 25 W

Answer: D

Short Answer Type Questions

Question.Two resistors of 10 Ω and 15 Ω are connected in series to a battery of 6 V. How can the values of current passing through them be compared?
Answer: In series, same current flows through each resistor. So, ratio of current is 1: 1.

Question. A wire of resistance 20 Ω is bent to form a closed square. What is the resistance across a diagonal of the square?
Answer: 

Question. Name a device that helps to maintain a potential difference across a conductor.
Answer: Cell or battery

Question. Write S.I. unit of resistivity.
Answer: Ohm-metre (Ωm).

Question. A 9Ω resistance is cut into three equal parts and connected in parallel. Find the equivalent resistance of the combination.
Answer: 

Question. Out of the two wires X and Y shown below, which one has greater resistance? Justify your answer.

Answer: Wire ‘Y’ has greater resistance as it has more length than wire ‘X’. It is because resistance of wire is directly proportional to the length of wire.

Question. V-I graph for two wires A and B are shown in the figure. If both wires are of same length and same thickness, which of the two is made of a material of high resistivity? Give justification for your Answer: 

Greater than slope of V-I graph, greater will be the resistance of given metallic wire. In the given graph, wire A has greater slope then B. Hence, wire A has greater resistance. For the wires of same length and same thickness, resistance depends on the nature of material of the wire, i.e.

Question.Define 1 volt. Express it in terms of SI unit of work and charge calculate the amount of energy consumed in carrying a charge of 1 coulomb through a battery of 3 V.
Answer: When 1 joule of work is done in carrying 1 coulomb of charge, from infinity to a point in the electric field, then potential at that point is called 1 volt. Potential difference between two points is

Question. How much current will an electric bulb draw from 220 V source if the resistance of the bulb is 1200Ω? If in place of bulb, a heater of resistance 100 Ω is connected to the sources, calculate the current drawn by it.
Answer: 

Question.The figure below shows three cylindrical copper conductors along with their face areas and lengths. Discuss in which geometrical shape the resistance will be highest.

Answer: 

Question. Find the current drawn from the battery by the network of four resistors Shown in the figure.

Answer: 

Question. B₁ B₂ and B₃ are three identical bulbs connected as shown in figure. When all the three bulbs glow, a current of 3A is recorded by the ammeter A.
Answer: 

(i) What happens to the glow of the other two bulbs when the bulb B1 gets fused?
(ii) What happens to the reading of A₁, A₂, A₃ and A when the bulb gets fused?
(iii) How much power is dissipated in the circuit when all the three bulbs glow together?
(i) Since B₁, B₂ and B₃ are in parallel, the potential difference across each of them will remain same. So when the bulb B₁ gets fused,B₁ ,B₂ and B₃ have the same potential and continues with the same energy dissipated per second, i.e. they will glow continuously as they were glowing before.
(ii) Resistance of the parallel combination when all the three bulbs are glowing

Since resistance of each arm is same and p.d. is also same, current divides them equally. So 1A current will pass through each bulb Bl and By
Therefore, ammeter A₁ and A₃ reads l A current while A₂ will read zero and ammeter A read 2 A current.
(iii) In parallel, total power consumed
Peq=P₁ +P₂ +P₃
So, when all the three bulbs glow together

Long Answer Type Questions

Question. Two wires A and B are of equal length and have equal resistance. If the resistivity of A is more than that of B, which wire is thicker and why? For the electric circuit given below calculate:

(i) Current in each resistor,
(ii) Total current drawn from the battery, and
(iii) Equivalent resistance of the Circuit
Answer: 

So, for different materials having same resistance per unit length, greater resistivity material wire has more cross-sectional area.
Hence, wire A is thicker than that of B.
(i) Current through each resistor

Question. (a)Two resistors R₁ and R₂ may form (i) a series combination or (ii) a parallel combination, and the combination may be connected to a battery of 6 volts. In which combination, will the potential difference across R₁ and across R₂ be the same and in which combination, will the current through R₁ and through R₂ be the same?
(b) For the circuit shown in this diagram, calculate

(i) the resultant resistance.
(ii) the total current.
(iii) the voltage across 7 Ω resistor.
Answer: (a) Potential difference across R₁ and R₂ is same in parallel combination of R₁ and R₂ and the current through R₁ and R₂ will be same when they are connected in series.

Question. A. Two identical wires one of nichrome and other of copper are connected in series and a current (I) is passed through them. State the change observed in the temperatures of the two wires. Justify your answer. State the law which explains the above observation.
B. An electric bulb is rated at 60 W, 240 V. Calculate its resistance. If the voltage drops to 192 V, calculate the power consumed and the current drawn by the bulb. (Assume that the resistance of the bulb remains unchanged.)
Answer: A. The resistivity of nichrome is more than that of copper so its resistance is also high. Therefore, large amount of heat is produced in the nichrome wire for the same current as compared to that of copper wire. Accordingly, more change in temperature is observed in the nichrome wire. This is explained by Joule’s law of heating. Joule’s law of heating: It states that the amount of heat produced in a conductor is

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