Q1. What is the SI unit of electric current?
a) Volt
b) Watt
c) Ampere
d) Ohm
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Correct Answer: c) Ampere
Explanation: The SI unit of electric current is the ampere (A). One ampere is defined as the flow of one coulomb of charge per second through a conductor. It is named after the French mathematician and physicist André-Marie Ampère.
Q2. Which of the following materials is commonly used as a conductor in electrical wires?
a) Rubber
b) Glass
c) Copper
d) Plastic
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Correct Answer: c) Copper
Explanation: Copper is commonly used as a conductor in electrical wires due to its excellent electrical conductivity, high ductility, and corrosion resistance. It is an ideal material for transmitting electrical energy efficiently over long distances.
Q3. Electric current is defined as the flow of:
a) Electromagnetic waves
b) Electrons
c) Protons
d) Neutrons
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Correct Answer: b) Electrons
Explanation: Electric current is defined as the flow of electric charge carriers, typically electrons, through a conductor. When a potential difference is applied across a conductor, electrons move from areas of higher potential to lower potential, creating an electric current.
Q4. The rate of flow of electric charge through a conductor is measured in:
a) Ohms
b) Volts
c) Amperes
d) Watts
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Correct Answer: c) Amperes
Explanation: The rate of flow of electric charge through a conductor is measured in amperes (A). One ampere is equivalent to one coulomb of charge passing through a point in one second.
Q5. Which of the following factors affects the resistance of a conductor?
a) Length
b) Temperature
c) Material
d) All of the above
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Correct Answer: d) All of the above
Explanation: The resistance of a conductor is affected by its length, cross-sectional area, temperature, and the material from which it is made. Longer conductors have higher resistance, higher temperatures increase resistance, and different materials have different resistivities.
Q6. Which of the following is Ohm’s law?
a) V = IR
b) P = VI
c) I = V/R
d) R = V/I
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Correct Answer: c) I = V/R
Explanation: Ohm’s law states that the current (I) flowing through a conductor is directly proportional to the voltage (V) applied across it and inversely proportional to the resistance (R) of the conductor. Mathematically, it is represented as I = V/R.
Q7. A device used to measure electric current is called:
a) Voltmeter
b) Ammeter
c) Ohmmeter
d) Galvanometer
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Correct Answer: b) Ammeter
Explanation: An ammeter is a device used to measure electric current in a circuit. It is connected in series with the circuit so that the entire current flows through the meter, allowing it to measure the current accurately.
Q8. The electrical resistance of a conductor is directly proportional to its:
a) Length
b) Cross-sectional area
c) Material
d) Temperature
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Correct Answer: a) Length
Explanation: The electrical resistance of a conductor is directly proportional to its length. Longer conductors offer more resistance to the flow of electric current compared to shorter ones, as electrons have to travel a greater distance, experiencing more collisions.
Q9. Which of the following statements about electric current is true?
a) Electric current flows from positive to negative terminals in a circuit.
b) Electric current flows from negative to positive terminals in a circuit.
c) Electric current flows only in closed circuits.
d) Electric current flows at a constant rate in all conductors.
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Correct Answer: b) Electric current flows from negative to positive terminals in a circuit.
Explanation: In conventional current flow, electric current is considered to flow from the positive terminal to the negative terminal within a circuit. However, in reality, electrons (negative charge carriers) flow from the negative terminal to the positive terminal.
Q10. The total resistance in a series circuit is equal to:
a) The sum of the individual resistances
b) The product of the individual resistances
c) The reciprocal of the individual resistances
d) The square of the individual resistances
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Correct Answer: a) The sum of the individual resistances
Explanation: In a series circuit, the total resistance (R_total) is equal to the sum of the individual resistances (R_1 + R_2 + R_3 + …). This is because the current has to pass through each resistor in succession, resulting in the cumulative effect of resistance.