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Class 10 viva voce questions and answers are presented here to check your self how much you have prepared for your forthcoming examinations. These viva voce questions and answers are going to help you in the preparation of CBSE board exam and competitive entrance exam.

Q1. State Ohm’s law.

Ans. Ohm’s law states that if physical conditions like temperature remain constant or same the current(I) flowing through a conductor is directly proportional to the potential difference(V) applied across the ends.

i.e V ∞ I

or V = IR

Where R = resistance of the conductor

Q2.Is Ohm’s law true for all material?

Ans. It doesn’t hold good for electronic devices and non-ohmic resistance. Like semi-conductor diodes.

Q3.what is meant by E.M.F and potential difference of a cell

Ans. The maximum potential difference which exists between the terminals of a cell when no current is drawn from the cell is called e.m.f. (electromotive force)of the cell. On the other hand, when current is being drawn from the cell, the potential difference which exists between or across the terminals is called terminal potential difference or potential difference.

Q4.Define the potential difference. State whether the potential difference of a cell is smaller than its e.m.f.

Ans.The amount of work done when a single unit charge (1 coulomb) flows from one point to another point in a circuit.

Potential difference is smaller than e.m.f. is used in overcoming the internal resistance of a cell when current is drawn from it.

Q5.What is electric current?

Ans. The rate of flow of charge or electrons through a conductor is called electric current. Its SI unit is ampere (A).

Q6.Why copper wire is used in electric circuits?

Ans. Copper metal is a very good conductor of electricity. It has many free electrons to conduct current. It is not very expensive also.

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Q7.What is an ammeter? What do you mean by its least count?

Ans. An ammeter is an instrument to measure the magnitude of electric current flowing in a closed circuit. An ammeter is always connected in series.

By least count of any device or instrument, we mean the minimum quantity of the scale which can be read accurately in that instrument. For an ammeter, the least count is the minimum amount of current it can measure.

Q8.What is the battery eliminator?

Ans. A battery eliminator converts AC current to low voltage DC current.

Q9.What is voltmeter?

Ans. Its an instrument used to measure the potential difference across two points in a circuit carrying current.

Q10.Why a voltmeter is always connected in parallel?

Ans. A voltmeter has a very high resistance, hence it will allow a small amount of current it in a parallel circuit thus it will not interfere with the correct circuit measurements.

Q11.Define resistance.

Ans. The obstruction or oppose to the normal flow of current by the conductor when current is flowing through it is called resistance. Its SI unit is ohm(Ω).

Q12.What is the effect of temperature on the resistance of a conductor?

Ans. The resistance of most of the metallic conductors increases with an increase in temperature.

Q13.State the relationship of length and surface area of a conductor with its resistance.

Ans. Resistance is directly proportional to the length of conductor and inversely proportional to the area of cross-section.

Where, R = resistance(Ω), l= legth of the conductor(in meter), A= area of cross-section in m²

ρ = resisitivity(Ohm-meter)

Q14.What is the drawback if lights (lamps) are connected in series?

Ans. The main drawback is that if one lamp fuses the rest of the lamps will also stop functioning as current supply will stop functioning as the current supply will stop or get disconnected.

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Q15.Why are we advised to remove the plug from the key as soon as readings or observations are noted down?

Ans. We are advised to do so because longer duration of flow of current through the circuit will cause heating of the conductor wire thus increasing its resistance, which will provide an error in readings.

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Q16. Is the equivalent resistance of parallel combination greater than the individual resistance?

Ans.No, its value is smaller than the individual resistance if placed in series or separately.

Q17.Why rheostat of low resistance is used?

Ans. A rheostat of low resistance keeps the option open for a large variation in resistance thus cause a variety of current flow in the circuit to take many readings.

Q18.If two resistors having resistances of 3Ω and 4Ω respectively are connected in parallel, what will be the net resistance in the circuit?

Ans. The given resistors are of 3Ω and 4Ω

Let the net resistance of both is R, then calculating the net resistance as following

R ≈1.71 Ω

Therefore the net resistance of the circuit is almost 1.71 Ω

Q19.What happens to the ray of light which passes through the optical center of the lens.

Ans. The ray of light which passes through the optical center of a lens, doesn’t deviate from its path.

Q20. State the nature of the image formed when an object is placed between F1 and F2 in front of the biconvex lens.

Ans. The image will be formed beyond 2F1 and it will be real, inverted, and magnified.

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Q21. Define the angle of deviation.

Ans. In the refraction of a light ray, the angle between the incident and emergent rays is known as angle of deviation.

Q22. Define the angle of emergent ray.

Ans. The ray of light after undergoing refraction within the glass prism emerges out from the opposite face of the prism from where it entered is called the emergent ray.

Q23.What is the drawback if lights (lamps) are connected in series?

Ans.The main drawback is that if one lamp fuses the rest of the lamps will also stop functioning as current supply will stop functioning as the current supply will stop or get disconnected.

Q24.Why are we adviced to remove the plug from the key as soon as readings or observations are noted down?

Ans.We are advised to do so because longer duration of flow of current through the circuit will cause heating of the conductor wire thus increasing its resistance,which will provide an error in readings.

Q25.Is the equivalent resistance of parallel combination greater than the individual resistance?

Ans.No,its value is smaller than the individual resistance if placed in series or separately.

Q26.Why rheostat of low resistance is used?

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Ans.A rheostat of low resistance keeps the option open for a large variation in resistance thus cause a variety of current flow in the circuit to take many readings.

Q27.Why are the incident and emergent rays parallel to each other in case of a rectangular glass slab?

Ans.As angle of incidence ∠i is equal to angle of emergence,hence ∠e both the rays are parallel to each other.

Q28.State snell’s law of refraction?

Ans. According to snell’s law,the ratio of the sine of the angle of refraction is a constant, for a light ray of a given colour and for a given pair of media.

i.e.

µ = constant,also known as refractive index.μ

Q29.What is lateral displacement of light?

Ans.lateral displacement is the distance by which an incident ray get shifted sideward while emerging out naturally without any bending or shifting. Its angle of refraction will be zero.

Q30.A ray of light is incident on a glass slab normally. What will happen to the emergent ray?

Ans. There will be no deviation of the path and the emergent ray will be the same as the incident ray, emerging out normally without any bending to shifting. Its angle of refraction will be zero.

Q31. A ray of light traveling in a denser medium meets the surface of a rarer medium. How will it bent?

Ans.The ray while entering the second (rarer) medium at the point of the incident will bend away from the normal.

Q32. Define the angle of deviation.

Ans. It is the angle between the incident ray and the emergent ray, it is denoted by ‘d’ or D or ∂.

Q33. Which colour has the longest wavelength in VIBGYOR?

Ans. Red color.

Q34. Which color bend the most while emerging out after dispersion through a prism?

Ans. Violet colour.

Q35.What causes dispersion?

Ans. Different colours have different velocities while passing through a glass medium. They have different refractive indices(µ) . Hence the degree to which each color deviates inside the prism is also different. Hence a beam of white light undergoes dispersion.

Q36. State the relationship between ∠i (incident angle) and ∠A(angle of prism) of an optical glass prism.

Ans. ∠i + ∠e = ∠A + ∠δ

Where ∠i = angle of incidence, ∠e = angle of convergence, ∠A = angle of prism, ∠δ =angle of deviation

Q37. Can you explain why no dispersion is observed in case of a refraction of light through a glass slab?

Ans. A glass slab is a combination of two equal sizes and shaped prism oppositely arranged at their surfaces. Here a ray of light first gets dispersed within the slab but again recombine from its constituent colours to single beam of white light while emerging out.

Q38. In an equilateral prism, determine the angle of emergence, if the angle of incidence is 30°, and the angle of deviation is 28°.

Ans. The relationship between incident angle ∠i, angle of deviation ∠δ, angle of emergence ∠e, and angle of the prism ∠A is given by

Since the prism is equilateral, so the angle of prism ∠A = 60°

∠i + ∠e = ∠A + ∠δ

We are given incident angle ∠i = 30°, angle of deviation ∠δ=28°

30° + ∠e = 60° + 28°

∠e =88° – 30° = 58°

Therefore angle of emergence is = 58°

Q38.Where should an object be placed in order to get a virtual image by a convex lens?

Ans. In order to get a virtual image, the object should be placed between the optical center and the focal point of the convex lens.

Q39.Where should an object be placed in front of a convex lens to get its real and enlarged image?

Ans. The object should be placed at the point beyond the focal point of the convex lens for getting a real and enlarged image.

Q40. What is the resistivity or specific resistance of the material of the conductor?

Ans. Specific resistance or resistivity of a conductor is defined as the resistance of a conductor of a unit length and unit cross area. Its unit is ohn-meter.

Q41. What is equivalent resistance?

Ans. The equivalent resistance is the final resultant resistance offered by a group of resistance when placed in series or parallel combinations.

Q42.Find out the equivalent resistance of resistors 1Ω, 3Ω and 2.5Ω when that are placed in series.

Ans. Let the net resistance is R

R = 1 + 3 + 2.5 = 6.5Ω

Q43. What is the nature of the image formed by the plane mirror?

Ans.Virtual and erected

Q44.What type of image is formed by the convex lens?

Ans. Virtual and magnified when the object is placed between the optical center and focal point and real and inverted when the object is placed at other points on principal focus.

Q45.A point object is placed at a distance of 40 cm from a convex mirror of focal length 40 cm, determine the distance of the image created by it from the mirror.

Ans. The distance of the object from the mirror ,u = -40 cm

The focal length of the convex mirror,f = 40 cm

Let the distance of the image formed from the mirror is = v

Using the mirror formula

v = 20

Therefore, the image of the mirror will be formed at a distance of 20 cm behind the mirror

Q46. A concave mirror of focal length 15 cm can form a magnified, erect as well as an inverted image of an object placed in front of it . Justify this statement stating the position of the object with respect to the pole of the mirror in both the cases for obtaining the images.

Ans. For obtaining the magnified and erected image the object is placed between the focal point and the pole of the mirror and for obtaining the magnified and erected image the object is placed at the focal point or between the focal point and the pole.

Q47. What is the function of the retina in the human eye?

Ans. The retina in the human eye acts as a screen on which the image of the object is formed, the retina is made of light-sensitive cells known as rods and cones, these cells transform the image into electrical signals and then transported to the brain through the optic nerve and then the inverted image of the object is decoded by the brain to form erected image.

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