Class 10 Science · 35 questions · 34 with answers
A cell, a resistor, a key and ammeter are arranged as shown in the circuit diagrams of Figure12.1. The current recorded in the ammeter will be Fig. 12.1
This question refers to a figure in the original PDF.
(d) the same in all the cases
In the following circuits (Figure 12.2), heat produced in the resistor or combination of resistors connected to a 12 V battery will be Fig. 12.2
This question refers to a figure in the original PDF.
(a) same in all the cases
Electrical resistivity of a given metallic wire depends upon
(d) nature of the material
A current of 1 A is drawn by a filament of an electric bulb. Number of electrons passing through a cross section of the filament in 16 seconds would be roughly
(a) 10
Identify the circuit (Figure 12.3) in which the electrical components have been properly connected. Fig. 12.3 (a)
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(ii) (c)
What is the maximum resistance which can be made using five resistors each of 1/5 Ω?
(d) 1 Ω
What is the minimum resistance which can be made using five resistors each of 1/5 Ω?
(b) 1/25 Ω
The proper representation of series combination of cells (Figure 12.4) obtaining maximum potential is (a)
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(i) (b)
Which of the following represents voltage? Work done
(a) Current × Time
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
(c) 2A
A student carries out an experiment and plots the V-I graph of three samples of nichrome wire with resistances R 1, R 2 and R 3 respectively (Figure.12.5). Which of the following is true?
(c) R3 > R2 > R1
If the current I through a resistor is increased by 100% (assume that temperature remains unchanged), the increase in power dissipated will be
(c) 300 %
The resistivity does not change if
(c) the shape of the resistor is changed
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?
(c) Brightness of bulb B will be more than that of A
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
(c) 20 J
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?
(d) 5 A ELECTRICITY 93
Two resistors of resistance 2 Ω and 4 Ω when connected to a battery will have
(b) same current flowing through them when connected in series
Unit of electric power may also be expressed as
(a) volt ampere
A child has drawn the electric circuit to study Ohm’s law as shown in Figure 12.6. His teacher told that the circuit diagram needs correction. Study the circuit diagram and redraw it after making all corrections.
This question refers to a figure in the original PDF.
Three 2 Ω resistors, A, B and C, are connected as shown Fig. 12.6 in Figure 12.7. Each of them dissipates energy and can withstand a maximum power of 18W without melting. Find the maximum current that can flow through the three resistors?
This question refers to a figure in the original PDF.
Maximum current through resistor A = A = 3 A. Thus the maximum current through resistors B and C each 3× A = 1.5 A.
Should the resistance of an ammeter be low or high? Give Fig. 12.7 reason.
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Hint— It should be as close to zero as possible. Ideally it should be zero ohm. If it is non-zero and substantial it will affect the true current.
Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of 2 Ω in series with a combination of two resistors (4 Ω each) in parallel and a voltmeter across the parallel combination. Will the potential difference across the 2 Ω resistor be the same as that across the parallel combination of 4Ω resistors? Give reason.
Hint— Yes. Total resistance of the parallel combination is also 2 ohm (2 Ω ).
How does use of a fuse wire protect electrical appliances?
Hint— If a current larger than a specified value flows in a circuit, temperature of fuse wire increases to its melting point. The fuse wire melts and the circuit breaks.
What is electrical resistivity? In a series electrical circuit comprising a resistor made up of a metallic wire, the ammeter reads 5 A. The reading of the ammeter decreases to half when the length of the wire is doubled. Why? 94 E XEMPLAR P ROBLEMS – SCIENCE
Hint— Use the formula R = ρ . Also, V = R I. R is doubled while V remains unchanged. Hence current becomes .
What is the commercial unit of electrical energy? Represent it in terms of joules.
kW h. 1 kW h = 1000 W × 60 × 60s = 3.6 × 106 J
A current of 1 ampere flows in a series circuit containing an electric lamp and a conductor of 5 Ω when connected to a 10 V battery. Calculate the resistance of the electric lamp. Now if a resistance of 10 Ω is connected in parallel with this series combination, what change (if any) in current flowing through 5 Ω conductor and potential difference across the lamp will take place? Give reason.
(i) 5 Ω (ii) Hint— Calculate the total resistance of the circuit. There will be no change in current flowing through 5 Ω conductor. Also there will be no change in potential difference across the lamp either.
Why is parallel arrangement used in domestic wiring?
Hint— Provide the same potential difference across each electrical appliance.
B1, B2 and B3 are three identical bulbs connected as shown in Figure 12.8. When all the three bulbs glow, a current of 3A is recorded by the ammeter A.
This question refers to a figure in the original PDF.
Hint— (i) The glow of the bulbs B2 and B3 will remain the same. (ii) A1 shows 1 ampere, A2 shows zero, A3 shows 1 ampere and A shows 2 ampere (iii) P = V × I = 4.5 × 3 = 13.5 W .QPI#PUYGT3WGUVKQPU
Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another circuit another set of three bulbs of the same wattage are connected in parallel to the same source.
(a) Will the bulb in the two circuits glow with the same brightness? Justify your answer.
(b) Now let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason.
State Ohm’s law? How can it be verified experimentally? Does it hold good under all conditions? Comment.
Hint— Define Ohm’s law. Give details of experiment using a labelled circuit diagram. Support your answer giving relation between V and I and a graph depicting Ohm’s law. Ohm’s law does not hold under all conditions. Mention the conditions.
What is electrical resistivity of a material? What is its unit? Describe an experiment to study the factors on which the resistance of conducting wire depends.
Hint— Resistivity is numerically equal to the resistance of a wire of unit length having an unit area of cross-section. Its unit is ohm metre ( Ω m). Mention the dependence of resistance on length and area of cross section of the wire giving details of experiment using a circuit diagram.
How will you infer with the help of an experiment that the same current flows through every part of the circuit containing three resistances in series connected to a battery?
Hint— Describe the experiment using a circuit diagram. Give details showing that same current flows through each component in a series circuit. ANSWERS 165
How will you conclude that the same potential difference (voltage) exists across three resistors connected in a parallel arrangement to a battery? ELECTRICITY 95
Hint— Describe the experiment using a circuit diagram. Give details showing that same potential difference exists across each resistance in a parallel circuit.
What is Joule’s heating effect? How can it be demonstrated experimentally? List its four applications in daily life.
Hint— Joule’s heating effect, H = I2Rt. Describe the experiment using a circuit diagram. Applications: electric heater, geyser, laundry iron, electric oven, bulb, toaster, kettle etc. § 8×8 ·
Find out the following in the electric circuit given in Figure 12.9
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(a) Effective resistance of two 8 Ω resistors in the combination
Hint: Hint— R = R1 R2 / (R1+ R2) = ¨ ¸ =4Ω ©8+8¹ § 8×8 · (b) 1 A. Hint— I = V/R = 8/(4)+ ¨ ¸ = 8/8 =1A ©8+8¹ (c) 4 V. Hint— V = IR = 1×4 = 4 V (d) 4 W. Hint— P= I2R = 12 × 4 = 4 W (e) No difference. Hint— Same current flows through each element in a series circuit. 166 E XEMPLAR P ROBLEMS – SCIENCE %*#26'4 ANSWERS /WNVKRNG%JQKEG3WGUVKQPU