CBSE Class 10 Science Chapter 12 Electricity Very Short Answer Questions
Question 1. In an electric circuit, state the relationship between the direction of conventional current and the direction of flow of electrons.
Answer: The direction of conventional current is opposite to the direction of the flow of electrons.
Question 2. Write a relation between heat energyproducedin a conductor when a potential difference Vis applied across its terminals and a current flows through for
Answer: Heat produced, H = Vlt.
Question 3. How will the resistivity of a conductor change when its length is tripled by stretching it?
Answer: The resistivity of a metallic conductor does not depend on the length of the wire, so it will remain the same.
Question 4. Why is a series arrangement not used for connecting domestic electrical appliances in a circuit?
Answer: If anyone stops working due to some reason, others will also stop working.
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Question 5. The radius of the conducting wire is doubled. What will be the ratio of its new specific resistance to the old one?
Answer: 1: 1, as it depends on the nature of the material only.
Question 6. State which has a higher resistance—a 50 W or a 25 Wlamp bulb and how many times?
Answer: We know that \(\mathrm{R}=\frac{\mathrm{V}^2}{\mathrm{P}} \quad \text { or } \quad \mathrm{R} \propto \frac{1}{\mathrm{P}}\)
Thus, a 25 W lamp has double the resistance of a 50 W lamp.
Question 7. A bulb gets dimmer for a moment when a geyser connected across the same source is
switched on. Why?
Answer: The geyser draws a heavy current for a moment which causes a potential dropin the line. Due to this, the bulb gets dimmer.
Question 8. Why is an ammeter likely to burn, if you connect it in parallel?
Answer: If an ammeter is connected in parallel, the resultant resistance of the circuit decreases and more current passes through the instrument. Hence, the ammeter is likely to burn out.
Question 9. What happens to the resistance of a conductor when temperature is increased?
Answer: Its resistance increases.
Question 10. What is the resistance of an electric arc lamp, if the lamp uses 20 A when connected to a 220-volt line?
Answer: \(\mathrm{R}=\frac{\mathrm{V}}{\mathrm{I}}=\frac{220}{20}=11 \mathrm{ohm}\)
Question 11. Define one watt.
Answer: The power expended by a source through it under a potential difference of 1 volt.
Question 12. The power of a lamp is 60 W. Find the energy in joules consumed by it in Is.
Answer: Energy consumed = P x t
=60×1
=60
Question 13. State a difference between the wire used in the element ofan electric heater and in a fuse wire.
Answer: The wire used in the element ofan electric heater has a very high resistance while that in a fuse wire has a low resistance.
Question 14. In an electric circuit, state the relationship between the direction of conventional current and the direction of flow of electrons.
Answer: The direction of conventional current is opposite to the direction of the flow of electrons.
Question 15. Calculate the number of electrons constituting one coulomb of charge
Answer: Number of electrons = \(\frac{1 \mathrm{C}}{1.6 \times 10^{-19} \mathrm{C}}\)
= 0.625×1019
=6.25×1018
Question 16. A wire resistivity ‘p’ is pulled to double its length. What will be its new resistivity?
Answer: Resistivity remains the same i.e., ‘p’.
Question 17. Why is heat produced when a current is passed through a conductor?
Answer: During their motion, the electrons collide with one another and hence lose some kinetic energy. This loss of kinetic energy is dissipated as heat across the conductor.
Question 18. Why is tungsten metal selected for making filaments of incandescent lamps?
Answer: It is because tungsten has a high melting point.
Question 19. What will happen to the current in a circuit, if the fit resistance is doubled?
Answer: The current becomes half.
Question 20. Give two applications of the heating effect of current.
Answer: Electric Geyser and Electric Iron.
Question 21. What is meant by 1-ohm resistance?
Answer: The resistance of the conductor is said to be 1 ohm ifundor a potential difference of 1 volt a current of one ampere flows through the conductor.
Question 22. What is the resistance ofan ideal ammeter?
Answer: An ideal ammeter has zero resistance.
Question 23. Why is much less heat generated in long electric cables than in filaments of electric bulbs?
Answer: It is because the resistance of the filament of an electric bulb is much more than that of an electric cable.
Question 24. A resistance of 1 kg has a current of 0.25 A throughout it when it is connected to the terminal of a battery. What is the potential difference across the ends of a resistor?
Answer: From Ohm’s law,
V = IR = 0.25 x 1000 = 250 V.
Question 25. Why is manganin used for making standard resistors?
Answer: Mangan being an alloy has a low temperature coefficient of resistance.
Question 26. How is an ammeter connected in a circuit to measure current flowing through it?
Answer: It is always connected in series in a circuit through which the current is to be measured.
Question 27. 400 J of heat is produced in 4s in a 4 Q. resistor. Find potential differences across the resistor.
Answer: \(\begin{aligned}
& \mathrm{H}=\frac{\mathrm{V}^2 t}{\mathrm{R}} \\
& \mathrm{V}=\sqrt{\frac{\mathrm{RH}}{t}}=\sqrt{\frac{4 \times 400}{4}}=20 \mathrm{~V}
\end{aligned}\)
Question 28. Give one example of metal which is the best conductor ofheat.
Answer: Silver or Copper
Question 29. A given length of wire is doubled on itself and this process is repeated once again. By what factor does the resistance ofthe wire change?
Answer: Length \(\frac{\mathrm{L}}{4}\) and area 4 times
⇒ \(\mathrm{R}=-\frac{e \frac{\mathrm{L}}{4}}{4 \mathrm{~A}}=\frac{e \mathrm{~L}}{\mathrm{~A}} \times \frac{\alpha 1}{16}=\frac{1}{16} \times \frac{e \mathrm{~L}}{\mathrm{~A}}\)
Hence, the resistance changes by \(\frac{1}{16}\)
Question 30. Why do we use copper and aluminum wire for the transmission of electric current?
Answer: They have low resistivity and are good conductors of heat.
Question 31. What does an electric circuit mean?
Answer: An electric circuit is a continuous and closed path along which an electric current flows.
Question 32. Define the unit of current.
Answer: If one coulomb of charge flows through any conductor section in one second, then the current through it is said to be one ampere. 1A=1Cs-1
Question 33. Name a device that helps to maintain a potential difference across a conductor.
Answer: A battery
Question 34. What is meant by saying that a potential difference between two points is 1V?
Answer: The potential difference between two points is 1 volt if one joule of work moves a positive charge of one coulomb from one point to the other.
Question 35. How much energy is given to each coulomb of charge passing through a 6 V battery?
Answer: Energy given by battery
Charge x Potential difference
= 1C x 6 V
= 6
Question 36. Calculate the number of electrons constituting one coulomb of charge.
Answer:
Charge on one electron, e=1.6×10-19c
Total charge, Q=1Cs
Number of electrons, \(n=\frac{q}{e}\)
⇒ \(n=\frac{1 \mathrm{C}}{1.6 \times 10^{-19} \mathrm{C}}\)
n = 6.25 x 1018.