# CBSE – 10th Standard Science

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### Class 10 Question Bank Chapter 12 – Electricity

Q1. What does an electric circuit mean?

Ans. , A continuous and closed path of an electric current is called an electric circuit.

Q2. Define the unit of current.

Ans. The electric current is expressed by a unit called ampere (A), One ampere is constituted by the flow of one coulomb of charge per second, that is, 1 A = 1 C/1 s.

Q3. Define the unit of Electric current?

Ans. The SI unit of electric charge is coulomb (C), which is equivalent to the charge contained in nearly 6 × 1018   electrons.

Q4. Name a device that helps to maintain a potential difference across a conductor.

Ans. Variable resistor helps to maintain a potential difference without changing voltage.

Q5.  Name device that is used to change resistance in a circuit

Ans.. A device called rheostat is often used to change the resistance in the circuit.

Q6. How is a voltmeter connected in the circuit to measure the potential difference between two points?

Ans.  The potential difference is measured by the voltmeter A voltmeter is always connected parallel to the circuit.

Q7. What is meant by saying that the potential difference between two points is 1 V?

Ans. It means One volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to the other. Therefore, 1 volt = 1 joule /1 coulomb , 1 V = 1 J C–1.

Q8. What is ohm’s law?

Ans. Ohm’s law says that the potential difference across the ends of a resistor is directly proportional to the current through it, provided its temperature remains the same.

Q9. On what factors does the resistance of a conductor depend?

Ans. The resistance of the conductor depends on its length, on its area of cross-section, and on the nature of its material

Q10. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?

Ans. As cross section is inversely proportionate to current it flows more easily in a thin wire then thicker wire of the same material because the cross section of wire is less then thicker wire.

Q11. Why are coils of toasters and electric irons made of an alloy rather than a pure metal?

Ans. Resistivity of alloy is higher and they do not oxidise  (burn) readily at high temperatures for this reason, they are commonly used in electric iron and toaster.

Q12. Which among iron and mercury is a better conductor?

Ans. Mercury has 94.0 × 10-8  Wm and iron has lesser 10.0 × 10-8 Wm resistivity thus iron is a better conductor.

Q13. Why is the tungsten used almost exclusively for filament of electric lamps?

Ans. Tungsten (melting point 3380°C) is used for making bulb filaments. The filament is strong and has high melting point, thermally isolated as much as possible.

Q14. Which gases are used in bulbs to prolong the filament life?

Ans. The bulbs are usually filled with chemically inactive nitrogen and argon gases to prolong the life of filament..

Q15. Why does the cord of an electric heater not glow while the heating element does?

Ans. If the electric circuit is purely resistive, that is, a configuration of resistors connected to the source energy continually gets dissipated entirely in the form of heat. This is known as the heating effect of electric current

Q16.. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?

Ans. A parallel circuit divides the current through the electrical gadgets. The total resistance in a parallel circuit is decreased This is helpful particularly when each gadget has different resistance and requires different current to operate properly.

Q17. Why is the series arrangement not used for domestic circuits?

Ans. In a series circuit the current is constant throughout the electric circuit it is impracticable to connect a bulb and a heater in series, because they need currents of widely different values, another disadvantage of a series circuit is that when one component fails the circuit is broken and none of the components works so it is not useful for domestic use.

Q18.. How does a charge flows inside a wire?

Ans. The electrons are able to travel through a perfect solid crystal smoothly and easily, when a steady current flows through a conductor, the electrons in it move with a certain average ‘drift speed’.