Question 10. A cylindrical conductor of length l and uniform area of cross section A has resistance R. Another conductor of length 2l and resistance R of the same material has area of cross section
Answer: (c) 2A
Question 11. A student carries out an experiment and plots the V-I graph of three samples of nichrome wire with resistances R1, R2 and R3 respectively. Which of the following is true?
Answer: (c) R3 > R2 > R1
Question 12. If the current I through a resistor is increased by 100% (assume that temperature remains unchanged), the increase in power dissipated will be
Answer: (c) 300%
Question 13. The resistivity does not change if
Answer: (c) the shape of the resistor is changed.
Question 14. In an electrical circuit three incandescent bulbs A, B and C of rating 40 W, 60 W and 100 W respectively are connected in parallel to an electric source. Which of the following is likely to happen regarding their brightness?
Answer: (c) Brightness of bulb B will be more than that of A
Question 15. In an electrical circuit two resistors of 2 Ω and 4 Ω respectively are connected in series to a 6 V battery. The heat dissipated by the 4 Ω resistor in 5 s will be
Answer: (c) 20 J
Explanation: Since, resistors are connected in series, thus total effective resistance in circuit = 2Ω + 4Ω = 6Ω
Therefore,electric current,I through the circuit `=(6V)/(6Ω)=1 A`
Now,voltage through,4Ω resistor
Now, given, time, `t = 5s`
Dissipation of heat by 4Ω
Since, there is no division of electric current when resistors are connected in series,
Thus, electric current, `I = 1A`
Since,`H= I^2 Rt`
Question 16. An electric kettle consumes 1 kW of electric power when operated at 220 V. A fuse wire of what rating must be used for it?
Answer: (d) 5A
Explanation: Given, power, P = 1 kW = 1000 W
Since, electric power, `P = V xx I`
Or, `1000 W = 220V xx I`
Thus, an fuse of rating 5A must be used.
Question 17. Two resistors of resistance 2 Ω and 4 Ω when connected to a battery will have
Answer: (b) same current flowing through them when connected in series
Question 18. Unit of electric power may also be expressed as
Answer: (b) kilowatt hour
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