Time : 3 hrs Max Marks : 80. Section I

Transcription

1 ICSE Question Paper 07 Physics-X Fully Solved (Questions-Answers) Time : 3 hrs Max Marks : 80 General Instructions. Candidates are allowed additional 5 minutes for only reading the paper. They must not start writing during this time.. The time given at the head of this paper is the time allowed for writing the answers. 3. Attempt all questions from Section I and any four questions from Section II. 4. The intended marks for questions or parts of question are given in brackets (). Section I (40 Marks). (a) A brass ball is hanging from a stiff cotton thread. Draw a neat labelled diagram showing the forces acting on the brass ball and cotton thread. () (b) The distance between two bodies is doubled. How is the magnitude of gravitational force between them affected? () (c) Why is a jack screw provided with a long arm? () (d) If the power of a motor be 00 kw, at what speed can it raise a load of 50,000 N? () (e) Which class of lever will always have MA > and why? (). (a) Define heat capacity and state its SI unit. () (b) Why is the base of a cooking pan generally made thick? () (c) A solid of mass 50 g at 50 C is placed in 00 g of water at C, when the final temperature recorded is 0 C. Find the specific heat capacity of the solid. (Specific heat capacity of water = 4. J/g C) () (d) How is the refractive index of a material related to () (i) real and apparent depth? (ii) velocity of light in vacuum or air and the velocity of light in a given medium? (e) State the conditions required for total internal reflection of light to take place. ()

2 3. (a) Draw a ray diagram to show the refraction of a monochromatic ray through a prism when it suffers minimum deviation. () (b) The human ear can detect continuous sounds in the frequency range from 0 Hz to 0,000 Hz. Assuming that the speed of sound in air is 330 ms for all frequencies, calculate the wavelengths corresponding to the given extreme frequencies of the audible range. () (c) An enemy plane is at a distance of 300 km from a radar. In how much time, the radar will be able to detect the plane? Take velocity of radiowaves as ms. () (d) How is the frequency of a stretched string related to () (i) its length? (ii) its tension? (e) Define specific resistance and state its SI unit. () 4. (a) An electric bulb of resistance 500 Ω, draws a current of 0.4A. Calculate the power of the bulb and the potential difference at its end. () (b) State two causes of energy loss in a transformer. () (c) State two characteristics of a good thermion emitter. () (d) State two factors upon which the rate of emission of thermions depends. () (e) When does the nucleus of an atom tend to be radioactive? () Section II (40 Marks) 5. (a) A uniform half metre rule balances horizontally on a knife edge at 9 cm mark when a weight of 0 gf is suspended from one end. (i) Draw a diagram of the arrangement. (ii) What is the weight of the half metre rule? (3) (b) (i) A boy uses a single fixed pulley to lift a load of 50 Kgf to some height. Another boy uses a single movable pulley to lift the same load to the same height. Compare the effort applied by them. Give a reason to support your answer. (ii) How does uniform circular motion differ from uniform linear motion? (iii) Name the process used for producing electricity using nuclear energy. (3) (c) A pulley system with VR = 4 is used to lift a load of 75 kgf through a vertical height of 5 m. The effort required is 50 kgf in the downward direction. (g = 0 N kg ) Calculate (i) distance moved by the effort. (ii) work done by the effort. (iii) M.A. of the pulley system. (iv) efficiency of the pulley system. (4) 6. (a) (i) How is the transference of heat energy by radiation prevented in a calorimeter? (ii) You have a choices of three metals A, B and C, of specific heat capacities 900 J kg C, 380 J kg C and 460 J kg C respectively. To make a calorimeter, which material will you select? Justify your answer. (4) (b) Calculate the mass of ice needed to cool 50 g of water contained in a calorimeter of mass 50 g at 3 C such that the final temperature is 5 C. Specific heat capacity of calorimeter = 04. J/g C Specific heat capacity of water = 4. J/g C; atent heat capacity of ice = 330 J/g (3)

3 (c) (i) Name the radiations which are absorbed by greenhouse gases in the earth s atmosphere. (ii) A radiation X is focused by a particular device on the bulb of a thermometer and mercury in the thermometer shows a rapid increase. Name the radiation X. (iii) Name two factors on which the heat energy liberated by a body depends. (3) 7. (a) A lens forms an upright and diminished image of an object when the object is placed at the focal point of the given lens. (3) (i) Name the lens. (ii) Draw a ray diagram to show the image formation. (b) A ray of light travels from water to air as shown in the diagram given below Air Water (3) (i) Copy the diagram and complete the path of the ray. Given, the critical angle for water is 48. (ii) State the condition, so that total internal reflection occurs in the above diagram. (c) The diagram below shows a point source P inside a water container. Four rays A, B, C and D starting from the source P are shown upto the water surface. (4) Air A B C 48º D Water P (i) Show in the diagram, the path of these rays after striking the water surface. The critical angle for water air surface is 48. (ii) Name the phenomenon which the rays B and D exhibit. 8. (a) Name the factor that determines (i) loudness of the sound heard. (ii) quality of the note. (iii) pitch of the note. (3) (b) (i) What are damped vibrations? (ii) Give one example of damped vibration. (iii) Name the phenomenon that causes a loud sound when the stem of a vibrating tuning fork is kept pressed on the surface of a table. (3) (c) (i) A wire of length 80 cm has a frequency of 56 Hz. Calculate the length of a similar wire under similar tension, which will have frequency of 04 Hz. (ii) A certain sound has a frequency of 56 Hz and a wavelength of.3 m.. Calculate the speed with which this sound travels.. What difference would be felt by a listener between the above sound and another sound travelling at the same speed, but of wavelength.6 m? (4)

4 9. (a) (i) Name the colour code of the wire which is connected to the metallic body of an appliance. (ii) Draw the diagram of a dual control switch when the appliance is switched ON. (3) (b) (i) Which particles are responsible for current in conductors? (ii) To which wire of a cable in a power circuit, should the metal case of a geyser be connected? (iii) To which wire, should the fuse be connected? (3) (c) (i) Explain the meaning of the statement current rating of a fuse is 5A. (ii) In the transmission of power, the voltage of power generated at the generating stations is stepped up from kv to 3kV before it is transmitted. Why? (4) 0. (a) Answer the following questions based on a hot cathode ray tube. (i) Name the charged particles. (ii) State the approximate voltage used to heat the filament. (iii) What will happen to the beam when it passes through the electric field?(3) (b) State three factors on which the rate of emission of electrons from a metal surface depends. (3) (c) (i) What are free electrons? (ii) Why do they not leave the metal surface on their own? (iii) How can they be made to leave the metal surface? (State any two ways) (4) Answers. (a) Diagram showing the forces on the ball is given below, Point of suspension T(Tension) The forces acting on the brass ball are (i) weight (mg) of the brass ball is acting vertically downwards. (ii) tension (T) along the string. (b) et m and m are the two bodies separated by a distance r. Gravitational force between them is F Gm m = (i) r where, G = Gravitational constant. If the distance between two bodies is doubled, then new gravitational force between them will be Gm m F = ( r = Gm m (ii) ) 4r Now, if we divide Eq. (i) by Eq. (ii), we get F F O Gmm = r Gmm = 4 F 4r W (Weight) F = 4

5 Gravitational force will become one fourth, if the distance between two bodies is doubled. (c) In order to produce maximum turning effect of the screw jack by a force, the force is applied at a point on the body for which the distance from the axis is maximum. So, that the given force provides maximum torque to turn the screw jack. Numerically, Moment of force (torque, which is responsible for turning effect of the body) = Force applied perpendicular distance of force from axis of rotation. Therefore, the longer arm of the jack screw, the more force it can apply. (d) Given, power of the motor, P = 00 kw = W = 0 5 Watt and force, F = N. Now, from the definition of power, Work done F S P = = Time t S P = F = F v t Substituting the given values, we get = v v = = ms Hence, the motor can lift the load with a speed of ms. [QW = Force displacement] (e) In second class lever (class II ever), an effort arm is always greater than the load arm and the load is situated between fulcrum and effort. In this lever, the mechanical advantage and velocity ratio are always more than. The sketch of such lever is shown below E Effort oad arm Fulcrum ( F). (a) The quantity of heat given to any substance depends on its mass m, the change in temperature T and the nature of substance which is being warmed. To change the temperature of substance, a given quantity of heat is absorbed or rejected by it, which is characterised by a quantity known as heat capacity or thermal capacity. So, Thermal capacity is defined as the total amount of heat required to raise the temperature of a body by C. It is represented by S. Heat supplied to the body ( Q) Heat capacity ( S ) = Change in temperature ( T) Its SI unit is Joule/ C or Joule/K. Its older unit is cal/ C or cal/k or kcal/ C. (b) Thinner base pans definitely transmit heat from the burner to the food, as the base is made up of metal, which is good conductor of heat. But, when it comes to even cooking and maintaining regular heating without hot spots around the pans, it is convenient to use thicker base pans. Also, it has more thermal mass and it also retain its temperature i.e. the pan will stay at high temperature above and beyond the amount of heat that can immediately supplied by the heat source. (c) According to the question, Mass of solid = 50 g, Temperature of solid = 50 C, Mass of water = 00 g Temperature of water = C, Final temperature of mixture = 0 C Specific heat of water = cal/g/ C et specific heat capacity of solid = x According to the principle of thermal equilibrium, Q (heal lost) = Q C (heat gained) 50 x ( 50 0) = 00 ( 0 ) x = 9 Specific heat = = cal/g/ C 0.3 Capacity of solid = 4. J / g C = J/g C

6 (d) (i) When an object is placed under water (a any other medium) then observing it from outside the water (or medium) it appears to be raised above. The ratio of real depth and apparent depth is equal to the refractive index of the medium. Real depth Refractive index, µ = Apparent depth (ii) Relation between Refractive Index and Velocity of ight The refractive index of the medium is the ratio of the velocity of light in vacuum (or air) to the velocity of light in that medium. Velocity of light in vacuum ( c ) µ = Velocity of light in medium ( v ) (e) The necessary conditions for the total internal reflection are as follows: (i) The light must travel from a denser medium to a rarer medium. (ii) The angle of incidence must be greater than the critical angle ( i c ) media. for the pair of 3. (a) When a ray of light passes through a prism, it bends towards the thicker part of the prism. et the incident ray PQ falls on the face AB of prism and emerges out from the face AC as RS. P A N δ N G i e = i r r Q R N N S Here, PQ = Incident ray, QR = Refracted ray RS = Emergent ray, A = Angle of prism i = Angle of incidence, r, r = Angles of refraction e = Angle of emergence and δ = Angle of deviation. Angle of Deviation (δ) It is the angle which the emergent ray ( produced backward ) makes with the incident ray ( produced forward ). It depends upon the angle of prism. When angle of deviation is minimum, the prism is said to be in minimum deviation position. (b) Applying the formula, v = λ ν where, v = velocity of sound = 330 ms ν = frequency λ = wavelength of sound We have range of frequencies from 0 Hz 0, 000 Hz. Hence, for frequency ν = 0 Hz, we have (c) B C Sectional view of prism 330 λ λ = = = m For frequency ν = 0, 000 Hz, we have 330 = λ 0000 λ = = m As we know, speed = distance time Given, distance from the radar to the plane, d = 300 km = m velocity of radar, v = ms According to the formula, d v = t d 300, 000 t = = = = v s

7 (d) (i) Frequency of stretched string related with its length as: ν length (ii) Frequency of stretched string is related to tension in string as: v tension This means, frequency is inversely proportional to the length of the string and directly proportional to its tension. (e) Specific resistance or resistivity (ρ), of a conductor is defined as the resistance of a conductor of unit length and unit area of cross-section. From the factors affecting the resistance of a conductor, the resistance is given by, Its SI unit is ohm-m( Ω m) l RA Ωm R =ρ ρ = = = Ωm A l m Specific resistance or resistivity is the characteristic property of the material of the conductor and depends only on the nature of the material and temperature. 4. (a) Given, resistance of bulb R = 500 Ω current, I = 0.4 A power, P =? petential differance, V =? As we know power, P = I R = ( 04. ) 500 Power, P = 80 Watt Potential difference, V = IR = = 00V (b) The two causes of energy loss in a transformer are as follow: (i) Eddy Currents The alternating magnetic flux induces eddy currents in the iron core and causes heating. (ii) Resistance of the windings The wire used for the windings has some resistance and so energy is lost due to heat produced in the wire ( I R). (c) Two characteristics of a good thermion emitter are as follow: (i) It should have low work function (the minimum energy required by an electron to just escape from the metal surface.) i.e. lesser the work functions of the emitter, more conviently or easily, the electrons could be emitted with less energy applied. (ii) It should have large surface area. So, that more number of electrons could be emitted. (d) The rate of thermionic emission of electrons (number of electrons emitted per second) from a surface depends on the following factors, given as follow, (i) Nature of the Metal Surface ower the work function of the metal, greater is the rate of emission of electrons from its surface. (ii) Temperature of the Surface Higher the temperature of the surface, greater is the rate of emission of electrons from the surface. (e) Atoms with unstable nuclei are constantly changing as a result of the imbalance of energy within the nucleus. Instability of an atoms nucleus may result from an excess of either neutrons or protons. Radioactivity is the release of energy and matter. This means, when the nucleus loses a neutron, it gives off energy and becomes radioactive. 5. (a) (i) Diagram of the given arrangement is shown below, 0 cm 9 cm 00 cm (ii) Given, load = 0 gf Effort arm, d f = 9 cm. Weight of M = = 0 gf W m F (Knife edge) M (a weight)

8 Total length = metre = 50 cm (b) oad arm, d = 50 9 = cm According to principle of moment where, E = Effort d = E d W d = E d Substituting the given values, we get, 0 0 = E 9 E = 9 Effort = 448. gf E m E (i) Single movable pulley is used in the arrangement whose axis of rotation is not fixed. oad T Mechanical advantage, (MA) = = = [Q = T + T = T and E = T] Effort T distance moved by the effort and Velocity Ratio, ( VR ) = distance moved by the load de d = = =. [QdE = dand d d d d = ] Whereas, a single fixed pulley and its axis of rotation is fixed in position. oad T Mechanical advantage ( MA ) = = = Effort T [Qoad = T,Effort E = T, if pulley is not rotating] de d Velocity ratio ( VR ) = = = [Qd d E d d = and d = d] Efficiency of both the pulleys will be same. T E T T T E Single moveable pulley Single fixed pulley Hence, from the above, In the case of single movable pulley, MA > effort arm > load arm and in case of single fixed pulley. MA = load arm = effort arm Effort applied in single fixed pulley is less as compare single movable pulley. (ii) Uniform circular motion Uniform linear motion A. B. C. When a body moves in a circular path with uniform speed (constant speed). e.g. A car running at a constant speed 0 km/h and S-t graph is a straight line. Acceleration of a body moving in a circle is v r. Direction changes continuously. When a body travels equal distance in equal intervals of time, no matter how small the intervals may be. e.g. a stone tied to a thread. Acceleration of a body moving in a is a = v u t (iii) The process used for producing electricity using nuclear energy is known as nuclear fission. In nuclear reactor, 35 9 U breaks into two smaller fragments by bombardment of thermal neutron (slow moving low energy) e.g. 9 U + 0n Ba + Kr n + Q where, Q = energy released

9 (c) Given, VR =4, load = 75 kgf, load arm = 5 m, effort = 50 kgf Applying the formula, d = E d where = oad, d = load arm, E = effort and d E = effort arm Also, distance moved by effort de VR = = 4 = d E distance moved by load d 5 E (i) Distance moved by the effort, d E = 5 4 = 60 m (ii) Work done, W = F S = = 3000 J oad 75 (iii) MA = = Effort 50 = 3. 5 MA (iv) Efficiency, η = VR 00 = = 8. 75% 6. (a) (i) Calorimeter surface (outer) is highly polished, so that to minimise the heat loss due to radiation as polished metallic surfaces are poor absorber and poor emitter of heat. Calorimeters are made up of copper, which has highly polished surface. (ii) We shall select C whose specific heat capacity is 46 J/kg/ C to make a calorimeter because of its low specific heat capacity. Specific heat capacity means the total amount of heat required to raise the temperature of unit mass by C. ForC, the heat required is less to increase temperature of calorimeter. Hence, C should be selected. (b) ice (mg) m water (mg) mc t water (mg) 0 C water + and (50 g) calorimeter 50 g 3 C 3 C (c) From the principle of Calorimetery, Heat gained by ice = Heat lost by water + Heat lost by Calorimeter m + mc t = mwc w t + m c t. (i) cal cal where, m = mass of ice (suppose), = atent heat of ice = 330 J/g, t = Change in temperature = ( 5 0) = 5 C, final temperature = 5 C, c w = Specific heat of water = 4. J/g C, m w = mass of water = 50 g, m cal = mass of calorimeter = 50 g and c cal = specific heat of calorimeter = 04. J/g C Now, heat lost by water and calorimeter will be = ( 3 5) ( 3 5) = = 50 7 ( ) = Now, according to relation (i), we have m m 4. 5 = m ( ) = m 35 = m = 8630 = = = 53. g 35 Final temperature (5 C) (i) Mainly infrared radiations are absorbed by greenhouse gases. (ii) Infrared radiation. (iii) Heat energy liberated by a body depends on I. mass of the body II. rise/fall in temperature. 35

10 7. (a) (i) Concave lens. (ii) Ray diagram. P A A B F B O F Q AB = Object, A B = Image (b) (i) When the angle of incidence in water is at critical value, then the refracted ray lies along the boundary, having an angle of 90. O 90º C A i=48º (c) (ii) Necessary conditions for total internal reflection in the above figure are: I. The ray of light must travel from denser medium into a rarer medium. II. The angle of incidence in the denser medium must be greater than the critical angle for that pair of media. (i) Diagram showing total internal reflection Rarer medium (Air) Denser medium (water) A (ii) B exhibits refraction from denser to rarer medium. D exhibits total internal reflection as i > 48 ( ) of water. B r r O O O 3 D O 4 N i' i i c N N Partially C reflected rays i > i c Total Internal Reflection Water-air interface Totally reflected ray i c 8. (a) (i) oudness amplitude (ii) Quality (timbre) nature of wave form (iii) Pitch of note frequency (b) (i) The periodic vibrations of a body of decreasing amplitude in presence of resistive force are called the damped vibrations. The displacement-time graph for the damped vibrations is shown in the diagram below. The amplitude/displacement decreases exponentially with time. (ii) Simple pendulum s oscillation. (iii) Resonance It is a special case of forced vibration, when the frequency of an externally applied periodic force on a body is equal to its natural frequency, the body readily begins to vibrate with an increased amplitude. e.g. sympathetic vibrations of pendulums, frequency heard by tuning fork due to resonance with air etc.

11 (c) (i) As the frequency ( F) of wire is inversely proportional to its length ( l) i.e. F l So, for the same tension, we have, F l = F l Given, F = 56 Hz, F = 04 Hz and l = 80 cm = l l = 0 cm 04 Hence, the length of wire, which has frequency 04 Hz is 0 cm. (ii) Given, ν = 56 Hz, λ =. 3 m. Using the formula, v = ν λ = = m/s ~ 333 m/s. Now, new wavelength =. 6 m v = ν λ 333 = ν. 6 ν = = Hz. Frequency of above sound is 56 Hz, whereas frequency of this calculated sound is 8 Hz because speed of sound is same. 9. (a) (i) The colour coding of wires in a cable are as follow: Wires Old Convention Colour New Convention ive Red Brown Neutral Black ight blue Earth Green Green or Yellow (ii) Two-Way or Dual way Switch It means two or more switches in different locations to control one lamp. This figure illustrates that lights to be controlled from both locations. anding light Upstairs lighting circuit Protective Earth conductors omitted for clarity Gang, two way switches Three core and the earth (b) (c) Downstairs lighting circuit Hall light (i) Electrons orbiting the nucleus of an atom. (ii) Earth wire (iii) ive wire of the circuits (i) Current rating of fuse is 5A means, it is a safety device having short length of thin wire having low melting point of a particular amount of current 5A. Whenever current through this fuse exceeds the 5A limit, it will melt and break the circuit and save main circuit components from damage. (ii) Step up transformer increases the amplitude of alternating voltage from kv to 3 kv before it is transmitted to get better efficiency with less loss of energy. 0. (a) (i) Fine beam of electrons. (ii) Battery of emf 6V. (iii) An electric field is produced between the two plates by keeping one plate at positive potential and the other at negative potential. The electron beam on entering the space between the plates, gets deflected towards the positive plate due to this presence of electric field.

12 (b) The rate of thermionic emission of electrons (number of electrons emitted per second) from a surface depends on the following factors are as follows (i) Nature of the Metal Surface ower the work function of the metal, greater is the rate of emission of electrons from its surface. (ii) Temperature of the Surface Higher the temperature of the surface, greater is the rate of emission of electrons from the surface. (iii) Surface Area of the Metal arger the surface area of the metal emitting the electrons, greater is the rate of emission of electrons. (c) (i) In metals, the electrons in the outer shells (valence electrons) are loosely bound to the atoms, hence they are free to move easily within the metal surface but cannot leave the metal surface. Such electrons are called free electrons. (ii) Because they are loosely bound to the atoms due to attractive pull of the metal surface. (iii) Two ways in which electrons in the valence shell can be freed are: I. Thermionic Emission sufficient thermal energy can be imparted to the free electrons by suitable heating, so that they come out of the metal. II. Photoelectric Emission It is the phenomenon of emission of electrons from the surface of metal when light radiations of suitable frequency fall on it.