15 extra multiple-choice questions for Electricity (10th Standard Science, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
If a current of 0.75 A flows through a conductor for 10 minutes, what is the total charge that passes through any cross-section of the conductor?
- A. 7.5 C
- B. 450 CCorrect
- C. 75 C
- D. 0.075 C
Explanation. The electric charge is calculated by multiplying current and time in seconds. Here, current is 0.75 A and time is 600 seconds, giving 450 C.
Q2
In an active electric circuit, what is the relationship between the conventional direction of electric current and the actual direction of electron flow?
- A. Conventional current flows in the same direction as the electron flow.
- B. Conventional current flows in the direction opposite to the electron flow.Correct
- C. Conventional current is perpendicular to the electron flow.
- D. There is no relationship between their directions.
Explanation. By convention, the direction of electric current is taken as opposite to the direction of flow of electrons, flowing from positive to negative terminal.
Q3
How much work is done in moving a charge of 4 C across two points in a circuit having a potential difference of 12 V?
- A. 3 J
- B. 0.33 J
- C. 48 JCorrect
- D. 16 J
Explanation. Work done is the product of potential difference and charge. Multiplying 12 V by 4 C gives a total work done of 48 J.
Q4
According to Ohm's law, the steady current flowing through a conductor is directly proportional to the potential difference across its ends under which of the following physical conditions?
- A. When temperature varies continuously
- B. At constant temperatureCorrect
- C. When temperature is kept at zero degrees Celsius
- D. Independent of temperature changes
Explanation. Ohm's law is valid only when physical conditions, particularly the temperature of the conductor, remain constant.
Q5
Which of the following statements is true regarding electrical resistivity of materials at constant temperature?
- A. It is higher for copper than for glass.
- B. It is a constant for a given material and its SI unit is ohm metre.Correct
- C. It increases as the length of the wire increases.
- D. Its SI unit is ohm per metre.
Explanation. Resistivity is a characteristic constant for a given material at a constant temperature, and its SI unit is ohm metre.
Q6
Three resistors of resistances 5 \(\Omega\), 15 \(\Omega\), and 20 \(\Omega\) are connected end-to-end in a series combination. What is the effective resistance of this system?
- A. Less than 5 \(\Omega\)
- B. Exactly 15 \(\Omega\)
- C. 40 \(\Omega\)Correct
- D. 3.75 \(\Omega\)
Explanation. For resistors in series, the effective resistance is the sum of individual resistances, which equals 40 ohms.
Q7
When resistors are connected in a parallel combination across a potential source, which electrical quantity remains the same across each resistor?
- A. Electric current
- B. Potential differenceCorrect
- C. Electrical power
- D. Both current and potential difference
Explanation. In a parallel combination, the potential difference across each resistor is equal to the potential difference of the source.
Q8
If the effective resistance of three identical resistors in series is S and their effective resistance in parallel is P, what is the ratio of S to P?
- A. 3
- B. 1/9
- C. 9Correct
- D. 1/3
Explanation. For three identical resistors, series resistance is three times the individual resistance, and parallel is one-third, making the ratio nine.
Q9
Why is an alloy of nickel and chromium (Nichrome) commonly used as the heating element in electrical appliances like electric irons and heaters?
- A. It has low resistivity and low melting point.
- B. It has high resistivity and is not easily oxidized at high temperatures.Correct
- C. It is a superconductor at room temperature.
- D. It is extremely cheap and melts easily.
Explanation. Nichrome has a high resistivity, a high melting point, and does not oxidize easily at high temperatures, making it ideal for heating elements.
Q10
Which of the following correctly describes the properties required for a fuse wire and a bulb filament respectively?
- A. Fuse wire: high melting point; Filament: low melting point
- B. Fuse wire: high resistance and high melting point; Filament: low resistance and low melting point
- C. Fuse wire: low melting point; Filament: high melting pointCorrect
- D. Both must have identical melting points and resistances
Explanation. A fuse wire must melt easily to break excess current (low melting point), whereas a filament must withstand high heat to glow (high melting point).
Q11
An electric motor has a power rating of 2.5 horsepower (hp). What is its equivalent power rating in watts?
- A. 1865 WCorrect
- B. 746 W
- C. 1492 W
- D. 2500 W
Explanation. One horsepower is equal to 746 watts. Therefore, 2.5 horsepower is equal to 2.5 times 746, which is 1865 watts.
Q12
How many Joules of energy are equivalent to 1 kilowatt hour (kWh) of electrical energy consumed?
- A. \(3.6 x 10^3 J\)
- B. \(3.6 x 10^5 J\)
- C. \(3.6 x 10^6 J\)Correct
- D. \(1.0 x 10^3 J\)
Explanation. One kilowatt hour is equal to 1000 watt hours, which equals 1000 watts times 3600 seconds, resulting in 3.6 million Joules.
Q13
In domestic electric circuits in India, what is the color of the insulation for the live wire and what is the potential of the alternating current supplied?
- A. Red insulation and 220 V potentialCorrect
- B. Black insulation and 110 V potential
- C. Green insulation and 220 V potential
- D. Red insulation and 110 V potential
Explanation. In India, the live wire has red insulation and the domestic alternating current is supplied at a potential of 220 V.
Q14
What is the primary role of the earth wire, which has green insulation, in domestic electrical circuits?
- A. To carry current to run low-power appliances like fans.
- B. To serve as a protective conductor that safe-guards users from electric shocks.Correct
- C. To regulate the frequency of the alternating current.
- D. To increase the effective resistance of the circuit during overloading.
Explanation. The earth wire provides a low resistance path to the ground, sending accidental leakage currents from a metallic appliance safely into the Earth.
Q15
Which of the following conditions occurs when a live wire comes directly in contact with a neutral wire, leading to a very small effective resistance and a large flow of current?
- A. Overloading
- B. Earthing
- C. Short circuitingCorrect
- D. Electromagnetic induction
Explanation. A short circuit occurs when a live wire directly contacts a neutral wire, causing resistance to drop and a very large current to flow.
