CBSE Class 10 Physics Electricity Worksheet Set 06

This second printable worksheet for Class 10 Physics Electricity has fill in the blanks, true or false statements and numericals with answers. It covers units, resistivity, series and parallel resistance, electrical power and the commercial unit of energy.

Fill in the Blanks

Question 1. Fill in the blank: The potential difference across the ends of a resistor is ________ to the current through it, provided its ________ remains the same.
Answer:
Directly proportional; temperature (Ohm's law).
In simple words: This is Ohm's law.

Teacher's Note:
1. V ∝ I at constant temperature.
2. The constant is the resistance.

Question 2. Fill in the blank: The resistance of a conductor depends directly on its ________, inversely on its ________, and also directly on the ________ of the conductor.
Answer:
Length; area of cross-section; resistivity (nature of the material). That is R = ρl/A.
In simple words: R = ρl/A.

Teacher's Note:
1. Write the formula to check.
2. Temperature also matters.

Question 3. Fill in the blank: The S.I. unit of resistivity is ________.
Answer:
Ohm-metre (Ω m).
In simple words: Resistivity is measured in Ω m.

Teacher's Note:
1. ρ = RA/l gives Ω m.
2. Not the same as ohm.

Question 4. Fill in the blank: The resistance of a wire is ________ proportional to the square of its radius.
Answer:
Inversely proportional, since R = ρl/(πr²).
In simple words: A thicker wire has less resistance.

Teacher's Note:
1. Area ∝ r².
2. R ∝ 1/A.

Question 5. Fill in the blank: Kilowatt is the unit of electrical ________ but kilowatt-hour is the unit of electrical ________.
Answer:
Power; energy.
In simple words: kW is power; kWh is energy.

Teacher's Note:
1. Energy = power × time.
2. 1 kWh = 3.6 × 10⁶ J.

Question 6. Fill in the blank: A fuse is a short piece of wire of high ________ and low ________.
Answer:
Resistance (resistivity) and melting point.
In simple words: A fuse wire heats up easily and melts easily.

Teacher's Note:
1. Made of a lead-tin alloy.
2. Connected in series.

Question 7. Fill in the blank: A fuse is connected in ________ to the ________ wire.
Answer:
Series; live wire.
In simple words: A fuse sits in the live wire in series.

Teacher's Note:
1. It carries the full current.
2. If it blows, the appliance is cut off.

Question 8. Fill in the blank: The unit of power is ________.
Answer:
Watt (W) = 1 joule per second.
In simple words: Power is measured in watts.

Teacher's Note:
1. 1 W = 1 V × 1 A.
2. 1 kW = 1000 W.

Question 9. Fill in the blank: One watt of power is consumed when 1 A of current flows at a potential difference of ________.
Answer:
1 volt (P = VI).
In simple words: 1 W = 1 V × 1 A.

Teacher's Note:
1. P = VI.
2. Check the units.

Question 10. Fill in the blank: 1 kW h = ________.
Answer:
3.6 × 10⁶ J.
In simple words: One unit is 3.6 million joules.

Teacher's Note:
1. 1000 W × 3600 s.
2. Commercial unit of energy.

Question 11. Fill in the blank: Power transmission is carried out at high ________ and low ________.
Answer:
Voltage; current, so that the loss of power (I²R) in the lines is small.
In simple words: High voltage and low current reduce the loss in the wires.

Teacher's Note:
1. P = VI is fixed.
2. Loss = I²R.

Question 12. Fill in the blank: The rate at which electric work is done is called ________.
Answer:
Electric power.
In simple words: Power is work per unit time.

Teacher's Note:
1. P = W/t.
2. Unit: watt.

True or False

Question 13. State whether true or false: The reciprocal of resistance is called specific resistance.
Answer:
False. The reciprocal of resistance is called conductance. Specific resistance is another name for resistivity.
In simple words: Specific resistance means resistivity.

Teacher's Note:
1. Do not confuse conductance and resistivity.
2. Unit of resistivity: Ω m.

Question 14. State whether true or false: The resistance of a wire is directly proportional to area.
Answer:
False. The resistance of a wire is inversely proportional to its area of cross-section (and directly proportional to its length).
In simple words: Thicker wire means less resistance.

Teacher's Note:
1. R = ρl/A.
2. Length: directly. Area: inversely.

Question 15. State whether true or false: The resistivity of alloys decreases with the rise in temperature.
Answer:
False. The resistivity of alloys increases (only slightly) with the rise in temperature.
In simple words: Alloys change little, but they do not decrease.

Teacher's Note:
1. Metals and alloys increase their resistivity when heated.
2. Alloys vary less than pure metals.

Question 16. State whether true or false: Pure tungsten has high resistivity and a high melting point (nearly 3000 °C).
Answer:
True. Tungsten melts at about 3380 °C, so it is used for the filament of bulbs.
In simple words: Tungsten is suitable for filaments.

Teacher's Note:
1. High melting point and resistivity.
2. Used with an inert gas.

Question 17. State whether true or false: A fuse is a thin wire which melts and breaks the electric circuit due to only high voltage.
Answer:
False. A fuse melts when the current in the circuit becomes too high (overloading or short circuit), not because of high voltage alone.
In simple words: A fuse responds to excess current.

Teacher's Note:
1. Heating effect depends on current: H = I²Rt.
2. Name overloading and short circuit.

Numerical Questions

Question 18. What current must flow if 0.24 coulombs is to be transferred in 15 ms?
Answer:
t = 15 ms = 15 × 10⁻³ s.
I = Q/t = 0.24/(15 × 10⁻³) = 16 A.
In simple words: Current is charge per second.

Teacher's Note:
1. Convert ms into seconds.
2. I = Q/t.

Question 19. How many electrons are flowing per second past a point in a circuit in which there is a current of 4 A?
Answer:
Charge per second Q = It = 4 × 1 = 4 C.
n = Q/e = 4 / (1.6 × 10⁻¹⁹) = 2.5 × 10¹⁹ electrons per second.
In simple words: A 4 A current carries 2.5 × 10¹⁹ electrons per second.

Teacher's Note:
1. n = Q/e.
2. e = 1.6 × 10⁻¹⁹ C.

Question 20. Calculate the amount of work done to draw a current of 8 A from a point at 100 V to a point at 120 V in 2 seconds.
Answer:
Charge Q = It = 8 × 2 = 16 C.
Potential difference = 120 − 100 = 20 V.
Work done W = QV = 16 × 20 = 320 J.
In simple words: Work = charge × potential difference.

Teacher's Note:
1. First find the charge moved.
2. Then use W = QV.

Question 21. A current of 200 mA flows through a 4 kΩ resistor. What is the p.d. across the resistor?
Answer:
I = 200 mA = 0.2 A; R = 4 kΩ = 4000 Ω.
V = IR = 0.2 × 4000 = 800 V.
In simple words: V = IR with SI units.

Teacher's Note:
1. Convert mA and kΩ.
2. The answer is in volts.

Question 22. A TV draws a current of 5 A from the 240 V supply line. What current will this TV draw when it is connected to 100 V supply line?
Answer:
R = 240/5 = 48 Ω.
I′ = 100/48 = 2.08 A.
In simple words: The current falls in proportion to the voltage.

Teacher's Note:
1. R is fixed.
2. I′ = I × (100/240).

Question 23. Calculate the resistance of a copper wire of length 2 m and area of cross section 10⁻⁶ m². Resistivity of copper is 1.7 × 10⁻⁸ Ω m.
Answer:
R = ρl/A = (1.7 × 10⁻⁸ × 2)/10⁻⁶ = 3.4 × 10⁻² Ω (0.034 Ω).
In simple words: A short thick copper wire has a very small resistance.

Teacher's Note:
1. Use R = ρl/A.
2. Keep the powers of ten together.

Question 24. A 6 Ω resistance wire is doubled up by folding. Calculate the new resistance of the wire.
Answer:
Folding in two halves the length and doubles the area.
R′ = ρ(l/2)/(2A) = R/4 = 6/4 = 1.5 Ω.
In simple words: Folding a wire in two gives one-fourth of its resistance.

Teacher's Note:
1. Length becomes l/2, area becomes 2A.
2. R′ = R/4.

Question 25. A 4 Ω wire is doubled on it. Calculate the new resistance of the wire.
Answer:
Doubling on itself gives half the length and twice the area, so R′ = R/4 = 4/4 = 1 Ω.
In simple words: Folding in two gives one-fourth of the resistance.

Teacher's Note:
1. Length l/2 and area 2A.
2. R′ = R/4.