LIGHT – REFLECTION AND REFRACTION
Q1. (i) Define the following terms in context of spherical mirrors.
(b) Centre of curvature
(c) Principal axis
(d) Principal focus
(ii) Draw ray diagrams to show the principal focus of a
(a) concave mirror and
(b) convex mirror
(iii) Consider the following diagram in which M is a mirror and P is an object and Q is its magnified image formed by the mirror.
State the type of the mirror M and one characteristic property of the image Q.
Q2. It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm.
(i) What should be the range of distance of an object placed in front of the mirror?
(ii) Will the image be smaller or larger than the object? Draw ray diagram to show the formation of image in this case.
(iii) Where will the image of this object be, if it is placed 24 cm in front of the mirror? Draw ray diagram for this situation also to justify your answer.
Show the positions of pole, principal focus and the centre of curvature in the above ray diagrams.
Q3. A student wants to project the image of a candle flame on the walls of school laboratory by using a lens.
(i) Which type of lens should he use and why?
(ii) At what distance in terms of focal length F of the lens should he place the candle flame, so as to get
(a) a magnified and
(b) a diminished image respectively, on the wall?
(iii) Draw ray diagrams to show the formation of the image in each case.
Q4. One half of a convex lens of focal length 10 cm is covered with a black paper. Can such a lens produce an image of a complete object placed at a distance of 30 cm from the lens? Draw a ray diagram to, justify your answer.
Q5. A 4 cm tall object is placed perpendicular to principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 15 cm. Find the nature, position and the size of the image.
Q6. What is meant by power of a lens? Define its SI unit. You have two lenses A and B of focal lengths +10 cm and -10 cm, respectively. State the nature and power of each lens. Which of the two lenses will form a virtual and magnified image of an object placed 8 cm from the lens? Draw a ray diagram to justify your answer.
Q7. Suppose you have three concave mirrors A, B and C of focal lengths 10 cm, 15 cm and 20 cm. For each concave mirror, you perform the experiment of image formation for three values of object distances of 10 cm, 20 cm and 30 cm. By giving reason, answer the following:
(i) For the three object distances, identify the mirror/mirrors which will form an image of magnification -1.
(ii) Out of the three minors identify the minor which would be preferred to be used for shaving purposes/ makeup.
(iii) For the mirror B draw ray diagram for image formation for object distances 10 cm and 20 cm.
Q8. A student wants to project the image of a candle flame on the walls of the school laboratory by using a mirror.
(i) Which type of mirror should he use and why?
(ii) At what distance, in terms of focal length ‘f’ of the mirror, should he place the candle flame to get the magnified image on the wall?
(iii) Draw a ray diagram to show the formation of the image in this case.
(iv) Can he use this mirror to project a diminished image of the candle flame on the same wall? State ‘how’ if your answer is ‘yes’ and ‘why not’ if your answer is ‘no.’
Q9. Draw a ray diagram in each of the following cases to show the position and nature of image formed when the object is placed:
(i) Between pole and focus of a concave mirror.
(ii) Between focus and centre of curvature of a concave mirror.
(iii) At the centre of curvature of a concave mirror.
(iv) Between infinity and pole of a convex mirror.
(v) At infinity from a convex mirror.
Q10. (i) Define focal length of a spherical lens.
(ii) A divergent lens has a focal length of 30 cm. At what distance should an object of height 5 cm from the optical centre of the lens be placed so that its image is formed 15 cm away from the lens ? Find the size of the image also.
(iii) Draw a ray diagram to show the formation of image in the above situation.
Q11. (i) Define power of a lens. Write its SI units.
(ii) You are provided with two convex lenses of focal length 15 cm and 25 cm, respectively. Which of the two is of larger power? Give reason for your answer.
(iii) A 20 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find Ute nature, position and size of the image. Also find its magnification.
Q12. (i) Draw a ray diagram to show the formation of image by a convex lens when an object is placed in front of the lens between its optical centre and principal focus.
(ii) In the above ray diagram mark the object-distance (u) and the image-distance (v) with their proper signs (+ve or – ve as per the new Cartesian sign convention) and state how these distances are related to the focal length (f) of the convex lens in this case.
(iii) Find the power of a convex lens which forms a real, and inverted image of magnification -1of an object placed at a distance of 20 cm from its optical centre.
Q13. (i) Two convex lenses A and B have powers P1 and P2 respectively and P2 is greater than P1 Draw a ray diagram for each lens to show which one will be more converging. Give reason for your answer.
(ii) A 2.0 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find the nature, position and size of the image. Also find its magnification.
Q14. (i) Define the following term related to spherical mirror.
(a) Radius of curvature
(c) Principal focus
(ii) Mention the differences between real image and virtual image.
Q15. (i) Draw ray diagrams and show the nature of images formed in the following cases, when
(a) object is placed between F and 2F in front of concave lens,
(b) object is placed between F and 2F in front of convex lens.
(ii) An object 50 cm is placed on the principal axis of a convex lens. Its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.
Q16. The image of an object placed at 60 cm in front of a lens is obtained on a screen at a distance of 120 cm from it. Find the focal length of the lens. What would be the height of the image, if the object is 5 cm high?
Q17. ( i) Two lenses have power of
(b) – 4D.
What is the nature and focal length of each lens?
(ii) An object is kept at a distance of 100 cm from each of the above lenses. Calculate the
(a) image distance and
(b) magnification in each of two cases.
HUMAN EYE AND THE COLOURFUL WORLD
Q1. (i) List three common refractive defects of vision. Suggest the way of correcting these defects.
(ii) About 45 lac people in the developing countries are suffering from corneal blindness. About 30 lac children below the age of 12-year suffering from this defect can be cured by replacing the defective cornea with the cornea of a donated eye. How and why can students of your age involve ‘themselves to create awareness about this fact among people?
Q2. What is atmospheric refraction? Use this phenomenon to explain the following natural events.
(i) Twinkling of stars.
(ii) Advanced sunrise and delayed sunset. Draw diagrams to illustrate your answers.
Q3. What is meant by scattering of light? Mention the factor on which it depends. Explain, why the colour of the clear sky is blue? An astronaut in space finds sky to be dark. Explain reason for this observation.
Q4. (a) Write the function of each of the following parts of human eye: Cornea, iris, crystalline lens, ciliary muscles.
(b) Millions of people of the developing countries of the world are suffering from corneal blindness. These persons can be cured by replacing the defective cornea with the cornea of a donated eye. A charitable society of your city has organized a campaign in your neighbourhood in order to create awareness about this fact. If you are asked to participate in this mission how would you contribute in this noble cause?
(i) State the objective of organizing such campaigns.
(ii) List two arguments which you would give to motivate the people to donate their eyes after death.
(iii) List two values which are developed in the persons who actively participate and contribute in such programmes.
Q5. (a) A student suffering from myopia is not able to see distinctly the objects placed beyond 5 m. List two possible reasons due to which this defect of vision may have arisen. With the help of ray diagrams, explain;
(i) Why the student is unable to see distinctly the objects placed beyond 5 m from his eyes.
(ii) The type of the corrective lens used to restore proper vision and how this defect is corrected by the use of this lens.
(b) If, in this case, the numerical value of the focal length of the corrective lens is 5 m, find the power of the lens as per the new Cartesian sign convention.
Q6. A person is unable to see distinctly the printed on a newspaper. Name the defect of vision he is suffering from. Draw ray diagram to Illustrate this defect. List its two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length.
Q7. (i) List three common refractive defects of vision. Suggest the way of correcting these defects.
(ii) About 45 lac people in the developing countries are suffering from corneal blindness. About 30 lac children below the age of 12 years suffering from this defect can be cured by replacing the defective cornea with the cornea of a donated eye. How and why can students of your age involve themselves to create awareness about this fact among people?
Q8. (i) Name the defect of vision in which the eye loses its power of accommodation due to old age.
(ii) The near point of a person suffering from hypermetropia is at 50 cm from his eye. What is the power of the lens needed to correct this defect/ (near point of normal eye is 25 cm)?
(iii) With the help of ray diagrams, show the formation of image by
(a) a hypermetropic eye.
(b) correction of hypermetropia by using an appropriate lens.
Q9. (a) What is presbyopia? State its cause. How is it corrected?
(b) Why does the Sun appear reddish early in the morning? Explain with the help of a labelled diagram.
Q10. (i) Define dispersion of light. How is scattering of light different from dispersion? Give one example of natural phenomenon based on each of these.
(ii) A beam of light consisting of red, blue and yellow colours is incident on the prisms as shown below. Complete the diagram to show refracted and emergent ray.
Q11. (a) Write an activity for observing scattering of light in colloidal solution.
(b) On the basis of this activity explain, why sky appears red at sunrise or sunset.
Q12. (i) Explain, how do we see different colours of an object?
(ii) Why is it so that some people cannot distinguish between different colours?
(iii) A chick wakes up with the sunrise and sleeps by sunset. How does it manage to do so?
Q13. (i) A doctor has prescribed a corrective lens of -4.2 D to a person suffering from defect of vision.
(a) Identify the defect from which he is suffering.
(b) Is the prescribed lens is diverging or converging? Show the nature of the lens with the help of a ray diagram.
(ii) The person wants to read a book placed at 20 cm, whereas near. point of his eye is 30 cm. Calculate the power of lens required.
Q14. (i) List the parts of the human eye that control the amount of light entering into it. Explain, how they perform this function?
(ii) Write the function of the retina in the human eye.
(iii) Do you know that the corneal-impairment can be cured by replacing the defective cornea with the cornea of the donated eye? How and why should we organise groups to motivate the community members to donate their eyes after death?
Q1. (i) Distinguish between the terms electrical resistance and resistivity of conductor.
(ii) A copper wire of resistivity 1.63 × 10-8 Ω-m has cross-section area of 10.3× 10-4 cm2. Calculate the, length of the wire required to make a 20Ω coil.
Q2. Two resistances when connected in parallel give resultant value of 2Ω, when connected in series the value becomes 9 Ω. Calculate the value of each resistance.
Q3. (i) Find the value of current I in the circuit given as below:
(ii) You have four resistors of 8 Ω each. Show how would you connect these resistors to have effective resistance of 8 Ω?
Q4. Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another set of three bulbs of the same wattage are, connected in parallel to the source.
(i) Will the bulb in the two circuits glow with the -same brightness? Justify your answer.
(ii) Now, let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit?
Q5. A household uses the following electric appliances;
(i) Refrigerator of rating 400 W for 10 h each day.
(ii) Two electric fans of rating 80 W each for 6 h daily. . .
(iii) Six electric tubes of rating 18 W each for 6 h daily.
Calculate the electricity bill, for the household for month of June, if cost of electrical energy is Rs.3 per unit
Q6. How will you conclude that the same potential difference (voltage) exists across three resistors connected in a parallel arrangement to a battery?
Q7. With the help of a circuit diagram prove that when a number of resistors are connected in parallel, the reciprocal of equivalent resistance of the combination is equal to the sum of the reciprocals of the individual resistances of the resistors.
Find the resistance between A and B in the following network.
Q8. (a) Two identical resistors each of resistance 10 ohm are connected in:
(i) Series, (ii) Parallel
in turn to a battery of 6V. Calculate the ratio of Power consumed by the combination of resistors In the two cases.
(b) List two factors on which the resistance of a conductor depends.
(c) Write a difference between an ammeter and voltmeter.
Q9. (a) Two students perform experiments on given resistors R1 and R2 and plot the following V-I graphs. If R1 > R2, which of the two diagrams correctly represent the situation on the plotted curves? Justify your answer.
(b) An electric lamp of 24 Ω and a conductor of 6 Ω are connected in parallel to a 12 V battery. Calculate:
(i) Total resistance,
(ii) Total current in the circuit,
(iii) Potential difference across the conductor.
Q10. Draw a circuit diagram for a circuit consisting of a battery of five cells of 2 volts each, a 5 Ω resistor, a 10 Ω resistor and a 15 Ω resistor, an ammeter and a plug key; all connected in series. Also connect a voltmeter to record the potential difference across the 15 resistor and calculate:
(i) The electric current passing through the above circuit and
(ii) Potential difference across 50 resistors when the key is closed.
Q11. What is meant by electric current? Name and define S.I. unit in a conductor electron are flowing from B to A. What is the direction of conventional current? Give justification for your answer.
A steady current of 1 Ampere flows through a conductor. Calculate the number of electrons that flow through any section of conductor in 1 second. (Charge on electron = 1.6 × 10-19 C)
Q12. (i) A wire of resistivity p is stretched to double its length which is its new resistivity. Give reason for your answer.
(ii) Draw a schematic diagram of a circuit consisting of a battery of three cells of 2V each, a 50 Ω resistor, 80 Ω resistor and 120 Ω resistor and a plug key all connected in series.
(iii) Two wires, one of copper and other of manganese have equal lengths and equal resistances. Which is thicker? (Given that resistivity of manganese is lower than that of copper.)
Q13. (i) What is meant by the statement that the resistance of a wire is 1 Q?
(ii) Two identical resistors each of resistance 12 Q are connected
(a) in series
(b) in parallel, in tum to a battery of 6 V.
Calculate the ratio of power consumed in the combination of resistors in the two cases.
(iii) What combination is used for connecting the circuit to measure the potential difference across two points?
Q14. Two conductors A and B of resistances 5Ω and 10 Ω respectively are first joined in parallel and then in series. In each case the voltage applied is 20 V.
(i) Draw the circuit diagram to show the combination of these conductors in each case.
(ii) In which combination will the voltage across the conductors A and 8 be the same?
(iii) In which arrangement will the current through A and B be the same?
(iv) Calculate the equivalent resistance for each arrangement.
Q15. (i) The potential difference between two points in an electric circuit is 1V. What does it mean? Name a device that helps to measure the potential difference across a conductor.
(ii) Why does the connecting cord of an electric heater does not glow while the heating element does?
(iii) Electrical resistivities. of some substances at 20°C are as given below:
Silver 1. 60 ×10-8 Q-m
Copper 1.62 ×10-8 Q-m
Tungsten 5.2 × 10-8 Q-m
Iron 10.0 ×10-8 Q-m
Mercury 94.0 ×10-8 Q-m
Nichrome 100 ×10-8 Q-m
Answer the following questions using following data.
(a) Among silver and copper, which one is a better conductor and why?
(b) Which material would you advise to be used in electrical heating devices and why?
Q16. Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another set, three bulbs of the same voltage are connected in parallel to the same source.
(i) Will the bulbs in the two circuits glow with the same brightness? Justify your answer.
(ii) Now let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reasons.
Q17. A wire is cut into three equal parts and then connected in parallel with the same source. How will its
(i) resistance and resistivity gets affected?
(ii) How would the total current and the current through the parts change?
MAGNETIC EFFECTS OF ELECTRIC CURRENT
Q1. Explain with the help of a labelled diagram, the distribution of magnetic field due to a current through a circular loop. Why is it that, if a current-carrying coil has n turns, the field produced at any point is n times as large as that produced by a single turn?
Q2. (i) Draw the magnetic field lines through and around a single loop of wire carrying electric current.
(ii) State whether an α-particle will experience any force in a magnetic field, if (α-particles are positively charged particles).
(a) It is placed in the field at rest.
(b) It moves in the magnetic field parallel to field lines.
(c) It moves in the magnetic field perpendicular to field lines. Justify your answer in each case.
Q3. Explain, why electric power transmitted at high voltages and low currents to distant places?
Q4. (i) What is a solenoid?
(ii) Draw the pattern of magnetic field formed around a current-carrying solenoid. Compare this field to that of a bar magnet.
(iii) Explain an activity to show that a current-carrying conductor experiences a force when placed in a magnetic field.
Q5. (i) A coil of insulated copper wire is connected to a galvanometer. What happens if a bar magnet is:
(a) Pushed into the coil?
(b) Withdrawn from inside the coil?
(c) Held stationary inside the coil?
Give reasons for your observation.
(ii) Mention one more method of inducing current in a coil.
Q6. (i) A stationary charge is placed in a magnetic field. Will it experience a force? Give reason to justify your answer.
(ii) On what factors does the direction of force experienced by a conductor when placed in a magnetic field depend?
(iii) Under what conditions is the force experienced by a current-carrying conductor placed in a uniform magnetic field maximum?
(iv) Name and state the rule which gives the direction of force experienced by a current carrying conductor placed in a magnetic field.
Q7. (a) Define electromagnetic induction.
(b) Two coils P and S are wound over the same iron core. Coil P is connected to battery and key and the coil S is connected to galvanometer. Write your observations when:
(i) Current in the coil P is started by closing the key.
(ii) Current continues to flow in coil P.
(iii)Current in coil P is stopped by removing the key.
Explain the reason for such observation.
Q8. (a) Draw a schematic labelled diagram of domestic electric circuit.
(b) Why is it necessary to provide-
(i) A fuse in an electric circuit
(ii) An earth wire to electric application metallic body? Explain.
Q9. (i) Explain what is the difference between a direct current and an alternating current. Write one important advantage of using alternating current.
(ii) An air conditioner of 2kW is used in an electric circuit having a fuse of 10A rating. If the potential difference of the supply is 220 V, will the fuse be able to withstand, when the air conditioner is switched on? Justify your answer.
Q10. (i) Explain two safety measures commonly used in electric circuits and appliances.
(ii) An electron enters a magnetic field at right angles to it as shown in figure. What will be the direction of force acting on the electron? State the rule which gives direction of force on electron.
(iii) If instead of electron, a neutron enters a field, what will be its direction of motion? Give reason for your answer.
Q11. (i) How does the strength of magnetic field due to current carrying conductor depends upon the current flowing and distance from the conductor?
(ii) α-particles are positively charged particles. State whether an a-particle will experience any force in a magnetic field, if
(a) it is placed in field at rest.
(b) it moves in the magnetic field parallel to field lines.
(c) it moves in the magnetic field perpendicular to the field lines. Justify your answer in each case.
Q12. Explain with the help of a labelled diagram, the distribution of magnetic field due to current-carrying coil that has n turns, such that the field produced at any point is n times as large as that produced by a single turn.
Q13. You are given the following current-time graphs from two different sources:
Now, answer the following questions:
(i) Name the type of current in two cases.
(ii) Identify any one source for each type of these currents.
(iii) What is the frequency of current in case (b) in India?
(iv) Use above graphs to write two differences between the current in two cases.