Direction (Q44 to Q48): In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following:
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.
44. Assertion: When a battery is short circuited, the terminal voltage is zero.
Reason: In short circuit, the current is zero.
45. Assertion: Conductors allow the current to flow through themselves.
Reason: They have free charge carriers.
1. Presence of argon prolongs the life of ____________ .
Answer: Filament of electric bulb
2. Work done on unit charge is called as ____________ .
Answer: Potential difference
3. Two resistors are in parallel when they have ____________ common points.
4. 746 watts make ____________ horse power.
5. Rheostat used in series in a circuit can make a bulb to glow with varying brightness. [True/False]
6. One common point and no sharing devices for that point are the conditions to be satisfied for two resistors to be in series. [True/False]
7. When bulbs are connected in series, the lower power bulb glows brighter. [True/False]
8. Nichrome is used for making standard resistances as it readily varies its resistance with temperature. [True/False]
9. The equivalent resistance between two diametrically opposite points as a wire of 10 Ω resistance is made a circle is 2.5 Ω. [True/False]
10. Devices of higher power used at home have lower resistance. [True/False]
11. 12 V means the work done to carry a unit charge from one point to another is 12 joule. [True/False]
12. Direction: Match Column I with Column II.
|Column I||Column II|
|(i) Fuse wires||A. Rheostat|
|(ii) Bulbs||B. Higher resistance|
|(iii) Higher power||C. Parallel|
|(iv) Potential divider||D. Series|
|(v) Lower current||E. Lower resistance|
(i) → D.
(ii) → C,
(iii) → E,
(iv) → A,
(v) → B
13. Name the charge responsible for the conduction in a conductor?
14. When two ends of a metallic wire are connected across the terminals of a cell, some potential difference is set up between its ends. In which direction, electrons are flowing through the conductors?
Answer: Direction of flow of electron: From a lower potential end of a metallic conductor to its higher potential end.
15. Electric current flows through a metallic conductor from its one end A to other end B. Which end of the conductor is at higher potential? Why?
Current always flow from a higher potential to a lower potential end of the conductor. So end ‘A’ of the conductor is at a higher potential.
16. Is there any charge movement in a wire under normal conditions?
Answer: No, net motion is zero even though individual charge can move.
17. Draw the following symbols:
(ii) Open key
(iii) Resistor of resistance R
18. What is ohm? Define it.
Answer: One ohm is that resistance offered by the wire carrying 1A of current when IV is applied across its ends.
19. What happens to resistance of a conductor when its area of cross-section is increased? [CBSE 2011]
Answer: Resistance decreases as R ∝ 1/A
20. The radius of 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 material only.
21. A given length of a wire is doubled on itself and this process is repeated once again. By what factor does the resistance of the wire change? [CBSE 2011]
Answer: Length becomes one-fourth of the original length and area of cross-section becomes four times that of original.
22. Name the scientist who first studied
(ii) resistance in detail.
(i) Andre – Marie, Ampere
(ii) Georg – Simon, Ohm.
23. Resistance of an incandescent filament of a lamp is comparatively much more than that when it is at room temperature. Why? [HOTS]
Answer: When bulb is switched on (i.e., incandescent state), the temperature of filament rises. As the temperature increases, the resistance of conductor also increases.
24. Why is magnanin used for making standard resistors?
Answer: Magnanin being an alloy has a low temperature coefficient of resistance.
25. A resistance of 1 k Ω has a current of 0.25 A throughout it when it is connected to the terminals of a battery. What is the potential difference across the ends of a resistor.
Answer: From Ohm’s law,
V = IR = 0.25 × 1000 = 250 V
26. Calculate the current in a circuit if 500 C of charge passes through it in 10 minutes.
Answer: Given: Q = 500 C, t = 10 min. = 10 × 60 = 600 s.
27. An electric iron draws a cu,.ent of 0.6 A when the voltage is 100 volt Calculate the amount of electric charge flowing through it in one hour.
As we know, Q = I × t
∴ Q = 0.6 × 3600 = 2160 C
28. Define the term resistivity. [DoE]
Answer: The resistance offered by a wire of unit length and unit cross-sectional area is called resistivity. It is expressed in terms of ohm-metre (Q-m).
29. Write S.I. unit of resistivity. [CBSE 2015]
30. 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 same.
31. When a battery is connected to a closed circuit, charge flow in the circuit almost instantaneously. Explain.
Answer: As soon as the battery is connected to the circuit and circuit is closed, a potential difference is felt over the entire circuit. This causes the charges begin to flow.
32. Why is closed path required for the flow of current?
Answer: It makes possible to move the electrons in a particular direction, so closed path is necessary for the flow of current.
33. Why is a series arrangement not used for connecting domestic electrical appliances in a circuit?
If any one stops working due to some reason, other will also stop working.
34. A torch bulb is rated at 1.5 V, 500 mA. Find its resistance.
Fill in the Blanks
1. The SI unit of current is ……… .
2. According to ……… Law, the potential difference across the ends of a resistor is directly proportional to the ……… through it, provided its remains constant.
3. The resistance of a conductor depends directly on its ……… , inversely on its ……… and also on the ……… of the conductor.
4. The SI unit of resistivity is ……… .
5. If the potential difference across the ends of a conductor is doubled, the current flowing through it, gets ……… .
2. Ohm’s, current, temperature
3. length, area of cross-section, material
4. ohm-metre (Ω m)