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ScienceClass 10CBSE

1. 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. (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 B2 gets fused? (iii) How much power is dissipated in the circuit when all the three bulbs glow together?

Potential difference does not get divided in parallel Hence glowing of other bulbs will not get affected when bulb one is fused. Ammeter A shows a reading of This means each of the Al. A2, and A3 show IA reading. R= V= 5 V = 1.5Ω I 3A Now P= I2R = (3A)2 x 1.5 Ω = 13.5 W

ScienceClass 10CBSE

1.      Why is parallel arrangement used in domestic wiring?

Parallel arrangement used in domestic wiring because it provides the same potential difference across each electrical appliance.

ScienceClass 10CBSE

1. 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.

Soln: Let R be the resistance of the electric In series total resistance = 5 + R I = v/r 1 = 10/5+R R = 5 ohm V across Lamp + conductor = 10 V V acoess Lamp = I × R = 1 * 5 = 5 Volt

ScienceClass 10CBSE

1.      What is the commercial unit of electrical energy? Represent it in terms of joules.

Commercial unit of electrical energy is kilowatt/hr 1 kw/hr = 1 kW h = 1000 W × 60 × 60s = 3.6 × 106 J

ScienceClass 10CBSE

1. 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?

Property of the conductor which resists the flow of electric current is called resistivity. Resistance for a particular material is unique. Resistance is directly proportional to length of conductor and inversely proportional to current flow. When length is doubled resistance becomes double and current flow reduces to half. This is the reason for the decrease in ammeter reading.

ScienceClass 10CBSE

1.      How does use of a fuse wire protect electrical appliances?

Fuse wire has great resistance than the main wiring. When there is significant increase in the electric current. Fuse wire melts to break the circuit. This prevents damage of electrical appliance.

ScienceClass 10CBSE

1. Unit of electric power may also be expressed as (a) volt ampere (b) kilowatt hour (c) watt second joule second

Soln: Answer is (b) kilowatt hour Explanation: Volt-ampere (VA) is the unit used for the apparent power in an electrical circuit. A watt second (also watt-second, symbol W s or W. s) is a derived unit of energy equivalent to the joule. The joule-second is the unit used for Planck's constant.

ScienceClass 10CBSE

1. Two resistors of resistance 2 Ω and 4 Ω when connected to a battery will have (a) same current flowing through them when connected in parallel (b) same current flowing through them when connected in series (c) same potential difference across them when connected in series different p

Soln: Answer is (b) same current flowing through them when connected in series Explanation: In series combination current does not get divided into branches because resistor receives a common current.

ScienceClass 10CBSE

1. 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? (a) 1 A (b) 2 A (c) 4 A (d) 5 A

Soln: Answer is (d) 5 A Explanation: P=V x I Or 1000 w = 220v x I I = 1000𝑤 220𝑣 = 5 A = 4.54 A

ScienceClass 10CBSE

1. 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 (a) 5 J (b) 10 J (c) 20 J (d) 30 J

Answer is (c) 20 J Explanation: Equivalent resistance of the circuit is R = 4+2 = 6Ω current, I= V/R) 6/6= 1A the heat dissipated by 4 ohm resistor is, H = IRt = 20J

ScienceClass 10CBSE

1. 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? (a) Brightness of all the bulbs will be the same (b) Brightness of bulb A will be the maximum (c) Brightness of bulb B will be more than that of A Brightness of bulb C will be less than that of B

Soln: Answer is (c) Brightness of bulb B will be more than that of A Explanation: Bulbs are connected in parallel so resistance of combination would be less than arithmetic sum of resistance of all the bulbs. So. there will be no negative effect on flow of current. As a result, bulbs would glow according to their wattage.

ScienceClass 10CBSE

1. The resistivity does not change if (a) the material is changed (b) the temperature is changed (c) the shape of the resistor is changed both material and temperature are changed

Soln: Answer is (c) the shape of the resistor is changed

ScienceClass 10CBSE

1. If the current I through a resistor is increased by 100% (assume that temperature remains unchanged), the increase in power dissipated will be (a) 100 % (b) 200 % (c) 300 % (d) 400 %

Soln: Answer is (c) 300 % Explanation: Heat generated by a resistor is directly proportional to square of current. Hence, when current becomes double, dissipation of heat will multiply by 2 =4. This means there will be an increase of 300%.

ScienceClass 10CBSE

1. A cylindrical conductor of length l and uniform area of crosssection A has resistance R. Another conductor of length 2l and resistance R of the same material has area of cross section (a) A/2 (b) 3A/2 (c) 2A (d) 3A

Soln: Answer is (c) 2A Explanation: P=𝑅𝐴 𝑙 When Length doubles P=𝑅𝐴 2𝑙 𝑅𝐴=𝑅𝐴 𝑙 2𝑙 A=2A

ScienceClass 10CBSE

1. Which of the following represents voltage? (a) Work done Current × Time (b) Work done × Charge (c) Work done × Time Current Work done × Charge × Time

Soln: Answer is (a) Work done Current × Time

ScienceClass 10CBSE

1. What is the minimum resistance which can be made using five resistors each of 1/5 Ω? (a) 1/5 Ω (b) 1/25 Ω (c) 1/10 Ω (d) 25 Ω

Soln: Answer is (b) 1/25 Ω Explanation: Minimum resistance is obtained when resistors are connected parallel 1 = 5 + 5 + 5 +5 +5= 25 Ω R R= 1 25Ω

ScienceClass 10CBSE

1. What is the maximum resistance which can be made using five resistors each of 1/5 Ω? (a) 1/5 Ω (b) 10 Ω (c) 5 Ω (d) 1 Ω

Soln: Answer is (d) 1 Ω Explanation: Maximum resistance is obtained when resistors are connected in series. R=1 + 1 + 1 + 1 + 1 5 5 5 5 5 = 5/5 = 1Ω

ScienceClass 10CBSE

1. 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) 1020 (b) 1016 (c) 1018 (d) 1023

Soln: Answer is (a) 1020 Explanation: I = Q/t Q= It Q= 1 x 16 Q= 16 q Q=ne n = Q/e n = 16 /1.6 x 10-19 n = 10 x 1019 n = 1020 electrons The number of electrons flowing is 1020 electrons

ScienceClass 10CBSE

1. Electrical resistivity of a given metallic wire depends upon (a) its length (b) its thickness (c) its shape nature of the material

Soln: Answer is (d) nature of the material

ScienceClass 10CBSE

1. Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet get deflected when a bar magnet or a current carrying loop is brought near it. Describe some salient features of magnetic lines of field concept.

Current carrying loops acts as bar magnets which have associated lines of field. This changes existing earth’s magnetic field and a deflection results. Magnetic field has both direction and magnitude. Magnetic field lines emerge from north pole and enter south pole. The magnetic field strength is represented diagrammatically by the degree of closeness of the field lines. Two values of net field cannot exist as a single point as field lines cannot cross each other. Only one value, a unique net value, can exist. If in a given region, lines of field are shown to be parallel and equispaced, the field is understood to be uniform.

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