CBSE X Science Effects of Current - EducareHut (Next Gen Knowledge Point)

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#1. 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.

A/2

3A/2

Resistivity of first conductior = (RA/l)
Resistivity of second conductor = (RA’/2l)

Resistivity of both material is same
so (RA)/(l) = (RA’/2l) => A’=2A

#2. Three resistors of 1 Ω, 2 ft and 3 Ω are connected in parallel. The combined resistance of the three resistors should be

greater than 3 Ω

less than 1 Ω

equal to 2 Ω

between 1 Ω and 3 Ω

#3. A fuse wire repeatedly gets burnt when used with a good heater. It is advised to use a fuse wire of

more length

less radius

less length

more radius

Explanation: (d) In order to get the working of heater properly, fused wire of higher rating must be used.

#4. Which of the following gases are filled in electric bulbs?

Helium and Neon

Neon and Argon

Argon and Hydrogen

Argon and Nitrogen

#5. When electric current is passed, electrons move from:

high potential to low potential.

low potential to high potential.

in the direction of the current.

against the direction of the current

#6. 1 mV is equal to:

10 volt

1000 volt

10^-3 volt

10^-6 volt

#7. Two wires of same length and area made of two materials of resistivity ρ1 and ρ2 are connected in series to a source of potential V. The equivalent resistivity for the same area is

Explanation: (a) For same length and area of cross-section R ∝ p.

For series combination, equivalent resistance is

Rs = R₁ R₂

⇒ Ps = ρ₁ ρ₂

#8. 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

10^20

10^16

10^18

10^23

Explanation: (a) Q = ne and Q = It

∴ ne = It

n=IT/e= (1×16)/(1.6×10^-19)

10²⁰

#9. A cell, a resistor, a key, and an ammeter are arranged as shown in the circuit diagrams. The current recorded in the ammeter will be

maximum in (i)

maximum in (ii)

maximum in (iii)

same in all the cases

Explanation :(d) Ammeter is always connected in series with in the circuit. The reading is independent from its location.

#10. In an electrical circuit, two resistors of 2 and 4 respectively are connected in series to a 6V battery. The heat dissipated by the 4 resistor in 5s will be

10J

20J

30J

Explanation:

Here, first resistor, R1 = 2Ω

And second resistor, R2 = 4Ω

Voltage of cell, V = 6V

Time taken = t = 5s

Total resistance of the circuit = R = R1 R2 = 2 4 = 6 Ω

Current, I = V/R = 6/6 = 1A

Heat dissipated by the 4Ω resistor in 5s is given as,

H = I²Rt

⟹ H = 1 x 1 × 4 × 5 = 20J

#11. A current of 1 A is drawn by a filament of an electric bulb. Number of electron passing through a cross-section of the filament in 16 seconds would be roughly

10^20

10^16

10^18

10^23

Current i= 1 A, time t=16s
Nuber of electrons=n
i=Q/t=ne/t
n=it/e=(1X16)/ (1.6*10^-19)=10^20

#12. The least resistance obtained by using 2 Ω, 4 Ω, 1 Ω and 100 Ω is

< 100 Ω

< 4 Ω

< 1 Ω

> 2 Ω

Explanation: (c) In parallel combination, the equivalent resistance is smaller than the least resistance used in the circuit.

#13. 1 kWh = ……….. J

3.6 × 10^-6 J

13.6 × 10^6 J

3.6 × 10^6 J

13.6 × 10^-6 J

#14. In the following circuits, heat produced in the resistor or combination of resistors connected to a 12 V battery will be

Same in all the cases

Maximum in case (i)

Maximum in case (ii)

Maximum in case (iii)

#15. The electrical resistance of insulators is

high

low

zero

infinitely high

#16. Electric potential is a:

scalar quantity

vector quantity

neither scalar nor vector

sometimes scalar and sometimes vector

#17. The resistivity of insulators is of the order of

10^-8 Ω-m

10^1 Ω-m

10^-6 Ω-m

10^6 Ω-m

#18. What is the minimum resistance which can be made using five resistors each of 1/5 Ω?

1/5

1/25

1/10

Explanation: The minimum resistance is obtained when resistors are connected in parallel combination.
Thus equivalent resistance obtained by connecting five resistors of resistance 1/5 Ω each, parallel to each other =

1/R= 1/R₁1/R₂1/R₃1/R₄1/R₅

R=1/25

#19. The proper representation of series combination of cells obtaining maximum potential is

iii

Explanation: Maximum potential is obtained when cells are connected in series such that, negative terminal of the cell is connected to the positive terminal of the second cell and so on, as shown in the following diagram.

#20. Electrical resistivity of a given metallic wire depends upon

Its length

Its thickness

Its shape

Nature of the material

Explanation: The resistivity of a material is constant for a particular temperature at a constant temperature.
Resistivity of material does not depend on length, thickness and shape of the material. It only depends on the temperature.

#21. Calculate the current flows through the 10 Ω resistor in the following circuit

1.2 A

0.6 A

0.2 A

2.0 A

Explanation: (b) In parallel, potential difference across each resistor will remain same. So, current through 10-Ω resistor

I = V/R=6/10 = 0.6 A

#22. Two wires of same length and area, made of two materials of resistivity ρ1 and ρ2 are connected in parallel V to a source of potential. The equivalent resistivity for the same length and area is

Explanation: (b) Equivalent resistance in parallel combination is

1/R_P =1/R₁ 1/R₂

For the same length and area of cross-section, R ∝ p (resistivity)

#23. The resistivity does not change if

the material is changed

the temperature is changed

the shape of the resistor is changed

both material and temperature are changed

Explanation: The resistivity depends on the nature of the material and the temperature. It does not depends on dimension of resistor.

#24. A cooler of 1500 W, 200 volt and a fan of 500 W, 200 volt are to be used from a household supply. The rating of fuse to be used is

2.5 A

5.0 A

7.5 A

10 A

Explanation: (d) Total power used, P = P₁ P₁ = 1500 500 = 2000 W.

Current drawn from the supply,I=P/V=2000/200=10A

#25. The temperature of a conductor is increased. The graph best showing the variation of its resistance is

Explanation: (a) Resistance is directly proportional to temperature of the conductor.

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