# 3 MARK QUESTIONS for Class 10 PHYSICS

LIGHT – REFLECTION AND REFRACTION

Q1.   What is meant by refractive index? If the speed of light in a medium is 2/3 rd of the speed of light in vacuum, find the refractive index of that medium.

Q2.  “The magnification produced by a spherical mirror is -3”. List four information you obtain from this statement about the mirror/image.

Q3.  The absolute refractive indices of glass and water are 4/3 and 3/2, respectively. If the speed of light in glass is 2 × 108 ms-1, calculate the speed of light in (i) vacuum (ii) water

Q4.         (i)  An object 1 cm high produces a real image 1.5 cm high when placed at a distance of 15 cm from a concave mirror. Calculate the position of the image and the magnification.

(ii)   Write two uses of concave mirrors.

Q5.  A   convex    lens    made    of   a   material of refractive index n2   is kept in a medium of refractive index n1. A parallel beam of light is incident on the lens. Draw the path of rays of light emerging from the convex lens, if

(i)  n1 < n2

(ii)  n1 = n2

(iii)  n1 > n2

Q6.  At what distance should an object be placed from a convex lens of focal length 18 cm to obtain an image at 36 cm from it? What will be the magnification produced in this case?

Q7.   Find the distance at which an object should be placed in front of a convex lens of focal length 10 cm to obtain an image of double its size.

Q8. Ravi is given lenses with powers +5D, -5D, +10D, -10D and   -20D. Considering a pair of lenses at a time, which two lenses will he select to have a combination of total focal length when two lenses are kept in contact in each case.

(i)  -10 cm

(ii)  20 cm

(iii) -20 cm

Q9. A 3 cm tall object is placed 18 cm in front of a concave mirror of focal length 12 cm. At what distance from the mirror should a screen be placed to see a sharp image of the object on the screen. Also calculate the height of the image formed.

Q10.The image of a candle flame placed at a distance of 30 cm from a mirror is formed on a screen placed in front of the mirror at a distance of 60 cm from its pole. What is the nature of the mirror?  Find its focal length. If the height of the flame is 2.4 cm, find the height of its image. State, whether the image formed, is erect or inverted.

Q11. A student wants to project the image of a candle flame on a screen 80 cm in front of a mirror by keeping the candle flame at a distance of 20 m from its pole.

(i) Which type of mirror should the student use?

(ii) Find the magnification of the image produced.

(iii) Find the distance between the object and its image.

(iv) Draw a ray diagram to show the image formation in this case and mark the distance between the object and its image.

Q12. A 5 cm tall object is placed at a distance of 30 cm from a convex mirror  of focal length 15 cm. Find the position, size and nature of the image formed.

Q13. If the image formed by a mirror for all positions of the object placed in front of it is always erect and diminished, what type of mirror is it? Draw a ray diagram to justify your answer. Where and why do we generally use this type of mirror?

Q14. Rohit wants to have an erect image of an object, using a converging mirror of focal length 40 cm.

(i) Specify the range of distance where the object can be placed in front of mirror. Give reason for your answer.

(ii) Will image be bigger or smaller than the object?

(iii) Draw a ray diagram to show the image formation in this case.

Q15. (i) What is the angle of incidence, when a ray of light falls on a spherical mirror from its centre of curvature?

(ii) Two concave mirrors have the same focal length but the aperture of one is larger than the other. Which mirror forms the sharper image and why?

(iii) A convex mirror is held in water. What change you will observe in its focal length?

Q16. State the laws of refraction of light. If the speed of light in vacuum is 3 × 108 m/s, find the speed of light in a medium of absolute refractive index 1·5.

Q17. (i)   Define the term magnification.  Write the formula for magnification of mirror explaining the symbols ‘used in the formula.

(ii) The magnification produced by a convex lens is -2. What is meant by this statement and also write the information regarding image obtained from it.

Q18. If the image formed by a lens for all positions of an object placed in front of it is always erect and diminished, what is the nature of this lens? Draw a ray diagram to justify your answer. If the numerical value of the power of this lens of 10 D, what is its focal length in the Cartesian system?

Q19. (i)  Draw a ray diagram to show the refraction of light through a glass slab and mark angle of refraction and the lateral shift suffered by the ray of light while passing through the slab.

(ii) If the refractive index of glass for light going from air to glass is 3/2, find the refractive index of air for light going from glass to air.

Q20. What is meant by power of a lens? You have three lenses L1, L2 and L3 of powers + 10D, +5D and- 10D respectively. State the nature and focal length of each lens. Explain which of the three lenses will form a virtual and magnified image of an object placed at 15 cm from the lens. Draw the ray diagram in support of your answer.

Q20. Calculate the distance at which an object should be placed in front of a convex lens of focal length 100 cm to obtain an erect image of double its size.

Q21. (i) A ray of light falls normally on a face of a glass slab. What are the values of angle of incidence and angle of refraction of this ray?

(ii) Light enters from air to a medium ‘X’. Its speed in medium ‘X’ becomes 1·5   × 108 m/s. Speed of light in air   3 × 108 m/s.  Find the refractive index of medium ‘X’.

Q22. (i) Water has a refractive index 1·33 and alcohol has refractive index 1·36. Which of the two medium is optically denser?  Give reason for your answer. Draw a ray diagram to show the path of a ray of light passing obliquely from water to alcohol.

(ii) The absolute refractive index of diamond is 2.42 and the absolute refractive index of glass is 1.50. Find the refractive index of diamond with respect to glass.

Q23.  (i) Is it possible that a convergent lens in one medium becomes divergent when placed in another medium?

(ii) Under what conditions there won’t be any refraction of light when it enters from one medium to another?

Q24.  Find the distance at which an object should be placed in front of a convex lens of focal length 10 cm to obtain an image of double its size.

Q25.  (i). What is the value of magnification when the size of image formed by a concave mirror is equal to the size of the object?

(ii) An object 2 cm high produces a real image 2.5 cm high, when placed at a distance of 15 cm from a concave mirror. Find

(a) the position of the image,

(b) focal length of the concave mirror.

Q26.   How far should an object be placed from a convex lens of focal length 20 cm to obtain its image at a distance of 30 cm from the lens? What will be the height of the image, if the object is 6 cm tall?

Q27.   An object of size 7.0 cm is placed at a distance of 27 cm in front of concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focused image can be obtained? Find the size and the nature of the image.

Q28.   A 5.0 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. By calculation determine

(i)  the position and

(ii) the size of the image formed.

Q29.   An object placed 45 cm from a lens forms an image on a screen placed 90 cm on the other side of the lens. Identify the type of the lens and find its focal length.

Q30.   A ray of light enters a diamond from air. If the refractive index of diamond is 2.42, what % (percent) is speed of light in diamond with that of speed in air?

HUMAN EYE AND THE COLOURFUL WORLD

Q1. Draw a labelled diagram of human eye. What is the significance of the blind spot?

Q2. List two main causes of a person developing nearsightedness. Show with the help of a ray diagram how this defect can be corrected.

Q3. Study the diagram given below and answer the questions that follows: (i) Which defect of vision is represented in this case? Give reason for your answer.

(ii) What could be the two causes of this defect?

(iii) With the help of a diagram show how this defect can be corrected by the use of a suitable lens?

Q4. Sun is visible 2 min before actual sunrise and 2 min after sunset. Give reason.

Q5.         (i)  Why does the power to see near objects as well as far off objects clearly diminish

(ii) The far point of a myopic eye is 60 cm. Find the focal length of the lens used to correct it.

Q6. With the help of ciliary muscles, the human eye can change its curvature and thus alter the focal length of its lens. State the changes that occur in the curvature and focal length of the eye lens while viewing:

(a) a distant object,

(b) nearby objects.

Explain, why a normal eye is not able to see distinctly the object placed closer than 25 cm, without putting any strain on the eye.

Q7. Due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens a certain defect of vision arises. Write the name of this defect. Name the type of lens required by such persons to improve the vision.  Explain the structure and function of such a lens.

Q8. (i) Make a ray diagram to show how the eye defect myopia is corrected by using a suitable lens.

(ii) State two reasons due to which this eye defect may be caused.

(iii) A person with   myopic eye cannot see objects beyond a distance of 1.5 m. What is the power of the lens required to correct the problem?

Q9. Explain why?

(i) Myopic person prefers to remove his spectacles while reading a book.

(ii) A hypermetropic person prefers to remove the spectacles while looking at the sky?

Q10. A person is unable to see objects nearer than 50 cm. He wants to read a book placed at a distance of 25 cm. Find the nature, focal length and power of the lens he requires for his spectacles.

Q11. What is meant by scattering of light? The sky appears blue and the sun appears reddish at sunrise and sunset. Explain these phenomena with reason.

Q12. How does refraction of light take place in the atmosphere? Explain the reason why stars appear to twinkle and the planets do not twinkle.

Q13.  Define angle of deviation. Why do different components of white light split up into spectrum when it passes through a triangular glass prism?  Show the angle of deviation for red colour when white light passes through a prism.

Q14. Name the phenomenon associated with the following:

(i) The sky appears blue.

(ii) Formation of a rainbow in the sky.

(iii) Twinkling of stars.

Q15. Explain in brief the reason for each of the following:

(i) The sun appears reddish during sun-rise.

(ii) At noon the sun appears white.

(iii) To an astronaut the sky appears dark instead of blue.

Q16. Describe an activity to show that the colours of white light split by a glass prism can be recombined to get white light  by another  identical  glass prism. Also, draw ray diagram to show the recombination of the spectrum of white light.

Q17. What is Tyndall effect? What is its causes? Name two phenomena observed in daily life which are based on Tyndall effect.

Q18.  Draw a labelled diagram of human eye. What is the significance of the blind spot and the yellow spot?

Q19.  Describe the formation of rainbow in the sky with the help of suitable diagram.

Q20.  List three common refractive defects of vision and suggest the way of correcting these defects.

Q21.   State the role of ciliary muscles in accommodation.

Q22.   Why we have two eyes to view the objects?

Q23.   What is the result of dispersion of white light?

Q24.   What is the difference in colours of the Sun observed during sunrise/sunset and noon?  Give explanation for each.

Q25.   How does the thickness of the eye lens change when we shift looking from a distant tree to reading a book?

Q26.  A person got his eyes tested. The optician prescription for the spectacles read.

Left eye= -3 D and right eye= -3.5 D

Discuss the defects of which a person is suffering.

Q27.  The power of a lens is +1.5 D. Name the type of defects of vision that can be corrected by using this lens. Find the focal length of the lens.

Q28. A person is able to see objects clearly only when these are lying at distance between  50 cm and 300 cm from his eyes. Name the kind of defects of vision he is suffering from.

Q29. What will be the angle of deviation through a prism angle 60 °, when angles of incidence and emergence are 45° each?

ELECTRICITY

Q1.  Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of 2 Ω in series with a combination of two resistor (4 Ω each) in parallel and voltmeter across the parallel combination. Will the potential difference across the 2 Ω resistor be the same as that across the parallel combination of 4 Ω resistors? Give reasons.

Q2. You have two electric lamps having rating 40 W, 220 V and 60 W, 220 V. Which of the two has a higher resistance? Give reason for your answer. If these two lamps are connected to a source of 220 V, which will glow brighter?

Q3. An electrical bulb is rated 40 W, 220 V. How many bulbs can be connected in parallel with each other across the two wires of 220 V line, if the maximum allowable current is 6 A?

Q4. An electric heater is rated at   2 kW. Calculate the cost of using it for 2 h daily for the month of September, if each unit costs Rs. 4.

Q5. (a) List the factors on which the resistance of a conductor in the shape of a wire depends.

(b) Why are metals good conductors of electricity whereas glass is a bad conductor of electricity? Give reason.

(c) Why are alloys commonly used in electrical heating devices? Give reason.

Q6. (a) Nichrome wire of length L and radius ‘R’ has resistance of 10Ω. How would the resistance of the wire change when:

(i)   Only length of the wire is doubled?

(b) Why element of electrical heating devices is made up of alloys?

Q7. Three resistors of 5 Ω, 10 Ω and 15 Ω are connected in series and the combination is connected to the battery of 30 V. Ammeter and voltmeter are connected in the circuit.  Draw a circuit diagram to connect all the devices in proper correct order.  What is the current flowing and potential difference across 10 Ω resistance?

Q8. Draw schematic diagram of a circuit consisting of a battery of five 2V cells, a 5 ohm, a 10 ohm and a 15-ohm resistor and a plug key, all connected in series.  Calculate the electric current passing through the above circuit when the key is closed.

Q9. (i) Define electric power.  A device of resistance R is connected across a source of V voltage and draws a current I. Derive an expression for power in terms of voltage and resistance.

(ii) An electric bulb is connected to a 220 V generator. The current is 0.5 A. What is the power of the blub?

Q10. (i) State one difference between Kilowatt and Kilowatt hour. Express 1kWh in joules.

(ii) A bulb is rated 5V, 500 mA. Calculate the rated power and resistance of the bulb when it glows.

Q11.What is an electric fuse? Why it is used in electric circuits? Should it be placed on neutral, wire or on live wire? Justify your answer.

Q12.Define electric power. An electric motor is rated at 2kW. Calculate the cost of using it for 2 hours daily for the month of September if each unit costs 6.00.

Q13. Give reason for the following:

(i) Why are copper and aluminium wires used connecting wires?

(ii) Why is tungsten used for filament of electric lamps?

(iii) Why is lead-tin alloy used for fuse wires?

Q14. Electrical resistivities of some substances, in ohm­meter, at 20°C are given as follows:

(i) Out of the silver and copper, which is a  better conductor of electric current and why?

(ii) Which substance is preferred to be used for electrical transmission lines? Give reason.

(iii) Name the material that you would advise to be used in the heater elements of electric heating device and why?

Q15. Explain the following:

(i) The elements of electric heating devices such as bread-toasters and electric iron are made of an alloy rather than of a pure metal.

(ii) Series arrangement is not used for domestic circuits.

(iii) Copper and aluminium wires are usually employed for electricity transmission.

Q16.Three resistors of 10 Ω,15 Ω and 20 Ω are connected in series in a circuit. If the potential drop across the 15 Ω resistor is 3 V, find the current in the circuit and potential drop across the 10 Ω resistor.

Q17.  A hot plate connected to a 220 V line as two resistance coils A and B, each of 22 Ω resistance. Calculate the amount of electric current flowing when these coils are:

(i) used individually.

(ii) connected in series.

(iii) connected in parallel.

Q18. A lamp rated 60W and an electric iron rated 800W are used for 6 hours everyday.  Calculate the total energy consumed in 30 days.

Q19. Five resistors are connected in a circuit as shown. Find the ammeter reading when circuit is closed. Q20. A 400 W refrigerator operates for 16 h per day. Calculate the cost to operate it for 30 days at 3.40 kWh.

Q21. A heater coil is rated 100 W, 200 V. It is cut in two identical parts and both parts are connected together in parallel to the same source of 200 V. Calculate the energy liberated per second in the new combination.

Q22.  If a 12 V battery is connected to the arrangement of resistances as shown below: Calculate

(i) the total effective resistance of the arrangement,

(ii) the total current flowing in the circuit.

Q23. (i) A current of 0.5A is drawn by a filament of electric bulb for 10 min. Find the amount of electric charge that flows through the circuit.

(ii) Should the resistance of an ammeter be low or high? Give reason.

Q24.   Aluminium wire has radius 0.25 mm and length of 75 m. If the resistance of the wire is l0Ω. Calculate the resistivity of aluminium.

Q24.       Find the current drawn from the battery by network of four resistors shown in the figure. MAGNETIC EFFECTS OF ELECTRIC CURRENT

Q1.  How does the strength of magnetic field due to a current-carrying conductor depend upon

(i)  distance from-the conductor?

(ii)   current flowing through the conductor?

Q2. Under what conditions permanent electromagnet is obtained, if a current-carrying solenoid is used?  Support your answer with the help of a labelled circuit diagram.

Q4.  What is an electric fuse?  What is its role in electric circuits? Should it be placed on neutral wire or on live wire?  Justify your answer.

Q5. What does the magnetic field pattern inside the solenoid indicate? State how this field be utilised to make an electromagnet. List two ways by which strength of this magnet can be increased.

Q6. Explain briefly two different ways to induce current in a coil. State the rule which determines the direction of induced current.

Q7. Explain whether an alpha particle will experience any force in a magnetic field if:

(i) It is placed in the field at rest.

(ii) It moves in the magnetic field parallel to field lines.

(iii) It moves in the magnetic field perpendicular to field lines.

Q8. How would the strength of magnetic field due to current carrying loop be affected if:

(i) Radius of the loop is reduced to half its original value?

(ii) Strength of current through the loop is doubled?

Q9. What is short-circuiting?   State one factor/condition that can lead to it. Name a device in the household that acts as a safety measure for it. State the principle of its working.

Q10. (a) Give the significance of the following in a domestic circuit:

(i) Electric meter

(ii) Earthing

Q11. List three factors which can cause overloading of domestic electric circuits.

Q12. The flow of current in a circular wire creates a magnetic field at its centre. How can existence of this field be detected? State the rule which helps to predict the direction of magnetic field.

Q13.  (i) What do you understand by the term short circuit? How does it occur?

(ii) What are the consequences of short circuit?

(iii) Give two examples for application of heating effect of electric current.

Q14.      A magnet AB is broken into two pieces. Point out the polarity of A, B, C and D. Q15.  A small valued resistance XY is connected across the ends of a coil. Predict the direction of induced current in the resistance XY when (i)  South pole of a magnet moves towards end A of the coil.

(ii)  South pole of a magnet moves away from end A of the coil.

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