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Electric Current Class 10 Extra Questions-answers

## TOPIC-1

### Electric current, electric circuit, voltage or electric potential, resistance and (Ohm’s law)

#### VERY SHORT ANSWER TYPE QUESTIONS [1 Mark]

Q. 1. Name the S.I. Unit of charge

Ans. The S.I Unit charge is coulomb (C).

Q. 2. What is the quantity of charge of an electron?

Ans. Charge on an electron is 1.6 x 10-19 Coulomb. (Negative charge)

Q. 3. Define electric current[CBSE 2012]

Ans. Electric charge flows through a cross-section of conductor per unit time

Q.4. State the S.I. unit of electric current. [CBSE 2012,

Ans. S.I Unit of electric current is Ampere or coulomb / second.

Q. 5. Define Ampere (A). [CBSE 2012]

Ans. Ampere is the rate of flow of one coulomb of electric charge through a surface per second.

Q. 6. Express one milliampere and microampere in an ampere unit.

Ans.

1 milliampere (mA) = 10-3

1 microampere (uA) = 10-6 A

7. Name the instrument that is used to measure the value of electric current. [CBSE 2010, 11, 12,]

Ans. Ammeter.

Q. 8. In an electric circuit, state the relationship between the direction of conventional current and the direction of flow of electrons. [CBSE 2011, 12]

Ans. In an electric circuit, the direction of the electric current is taken as opposite to the direction of the flow of electrons.

Q.9 Define the potential difference between two points in a conductor. [CBSE 2012]

Ans. The potential differences between two points in an electric field are defined as the amount of work done in moving a unit charge from one point to another. The potential difference between two points A or B.

Q. 10. What is represented by joule/coulomb?

Ans. It represented a potential difference.

Q. 11. What is S.I? Units of electrical potential? [CBSE 2007]

Ans. Volt or Joule/coulamb.

Q. 12. A charge of 2C moves between two plates, maintained at a potential difference of 1 V. What is the energy acquired by the charge?

Ans. W = Q x V

W = 2×1 = 2 Joule

Q.13 What is meant by the statement the potential difference between point A and B in an electric field is 1 Volt”? [CBSE 2007, 2010, 2011]

Ans.

1 Volt = 1 Coulomb

1 volt is the amount of work done to bring 1 C charge from point A to B in an electric field.

Q. 14. In what manner can ammeters be connected in an electric circuit? [CBSE 2011, 12]

Ans. Connected in series.

Q. 15. Name the instrument used to measure the potential difference. [CBSE 2011, 12]

Ans. Voltmeter.

Q. 16. How is a voltmeter connected in the circuit to measure the potential difference between two points?

Ans. Voltmeters must be connected in parallel.

Q. 17. Which of the two has a high internal resistance: voltmeter or ammeter?

Ans. The voltmeter has a higher internal resistance than an ammeter.

Q. 18. What are the essential components of an electric circuit?

Ans. Essential components of an electric circuit are :

(i) a voltage source (ii) a resistive electric device (iii) conducting wires (iv) a switch

Q. 19. What is electrical resistance?

Ans. It is a property of a material to oppose the flow of electric charge or electrons through it.

Q. 20. Give symbols of (i) an electric cell, (ii) battery of cells.

Ans. (i) An electric cell. (ii) The battery of cells.

Q. 21. What is an S.I. unit of electric resistance?

Ans. The S.I. unit of electric resistance is the ohm.

Q. 22. What is the name of a physical quantity which is equal to V/I?

Ans. Electrical resistance.

Q. 23. Define 1 ohm [CBSE 2010, 2011]

Ans.

The resistance of a conductor is 1 (ohm) when the potential at difference across the two ends of a conductor is 1 V and the current through it is 1 Å.

Q. 24. What is ohm’s law?

Ans. The potential difference across the ends of a resistor is directly proportional to the current flowing through it, at a constant temperature known as ohm’s low.

V αΙ       (at constnat temperature)

V = IR

Q. 25. What is the shape of the V-I graph for a metallic wire? Explain.

[CBSE 2010]

Ans. It is a straight line (inclined). Passing through origins. Because for metallic wire V α I.

Q. 26. What is the resistance of an electric bulb which is connected to a 220 V electric supply and has a current of 20 A flowing through it?

Ans.

Q. 27. The potential difference across the terminals of a cell is 1.5 volt. It is connected with a resistance of 30 Ω. Calculate the current flowing through the circuit. [CBSE 2013]

Ans

.[HOTS]

Ans. The ammeter consists of a wire of low resistance when connected in parallel, a large number of current passes throughout it hence get burnt… short-circuited.

Q. 32. Tap water conducts electricity whereas distilled water does not. Why? [HOT]

Ans. Tap water conducts electricity due to the presence of ions in it. But distilled water which is ion free does not conduct electricity.

Q. 33. What is electrical resistivity? [CBSE 2010]

Ans. It is the resistance offered by a cube of side 1 m when the current flows perpendicular to its opposite face.

Q. 34. What factors affect the resistivity of a material?

Ans. Factor affecting resistivity of a material :

(i) Nature of material and (ii) Physical condition like temperature and pressure.

Q. 35. On what factor does the resistance of a conductor depend?

[CBSE 2010, 12]

Ans. The factor on which resistance of a conductor depends are:

(i) Directly proportional to its length (R α l)

(ii) Inversely proportional to its area of cross-section

(iii) Also depends on temperature.

Q. 36. The resistance of a resistor is kept constant and potential difference across the two ends is decreased to half of its normal value. State that will occur in the current flow through it. [CBSE 2011]

Ans. As I α V (R = constant).

The current flowing through the conductor is also reduced to half of its previous value.

Q. 37. What happens to the current in a circuit if its resistance is double?

Ans.

(at constant V), the current is reduced to half of its previous value.

Q. 38. What happens to the resistance of a circuit if the current through it is doubled? [HOTS]

Ans. The resistance of the circuit does not depend on the current through it.

Q. 39. How does the resistance of a wire depend upon its radius?

Ans.

As

R is inversely proportional to the square of the radius.

Q. 40. Keeping the potential difference constant, the resistance of an electric circuit is doubled. State the change in the reading of an ammeter connected to the circuit. [CBSE 2011]

Ans. As

(at constant V), the current is reduced to one-half and the reading of the ammeter is also reduced to one half.

Q. 41. Two wires are of the same length, same radius, but one of them is copper (Cu) and the other is iron (Fe). Which will have more resistance? [HOTS]

Ans. As

but A and I are the same it depends only on resistivity (p) and it is more for iron (Fe). So iron has more resistance.

Q. 42. The length of a wire is doubled and its cross-sectional area is also doubled. What is the change in its resistivity? [CBSE 2009, 2011]

Ans. There is no change because the resistance of a material depends only on its nature.

Q. 43. Two wires of the same material and same length have radii r1 and r2. Compare their resistance. [HOTS]

Ans.

Q. 44. What happens to resistance when the length of the conductor is doubled without affecting the thickness of the conductor? [CBSE 2005]

Ans. As R α l, the resistance is increased to two-times of its initial value.

Q. 45. Mention any two factors on which the resistance of a cylindrical conductor depends. [CBSE, 2010 11, 12]

Ans. (i) Length of cylinder conductor (R & l)

(ii) The cross-sectional area of cylindrical conductor R

LA Q. 46. What happens to the resistance of a conductor when its temperature is decreased? [CBSE 2010]

Ans. As the temperature decreases, the resistance of the conductor decreases.

[i.e., Resistance (R) o temperature]

Q. 47. The voltage-current (V-I) graph of a metallic circuit at two different temperature T, and T, is shown in the figure. Which of the two temperatures is higher and why? [CBSE 2011]

Ans. As the temperature increases, the resistance of the conductor increases. Thus, temperature T is higher.

Q. 48. What is The S.I.unit of resistivity?

Ans. Ohm-metre (Ohm-m)

Q. 49. Why are copper wires used as connecting wires?

Ans. The electrical resistivity of copper is low.

Q. 50. A wire of resistivity ρ is stretched to double its length, what is its new resistivity?

Ans. Resistivity (p) remains the same because resistivity depends on the nature of the material.

Q. 51. Which material is the best conductor?

Ans. Silver

Q. 52. The following table gives the value of electrical resistivity of some materials: [CBSE 2005]

Which one is the best conductor of electricity out of them?

Ans. Silver, due to least resistivity.

Q. 53. What is rheostat?

Ans. The device is used to change the resistance in the circuit.

Q. 54. What is variable resistance?

Ans. Variable resistance is a component used to regulate the current without changing the voltage source.

Q. 55. What is the source of the electric charge?

Ans. cells or batteries.