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Monday, January 6, 2014

Let the resistance of an electrical component remains constant while the potential difference across the end of the component decreases to half of its former value. What change will occur with current through it?
What is the difference between real image and virtual image?
List three sources of magnetic fields.
What is the relation between joule and Kwh (kilowatt hour)?
A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
State ohm’s law. Draw a graph between voltage and current for a metallic conductor. Define resistivity and give its S.I unit. How does resistivity change with temperature?
The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?
(a) Between the principal focus and the centre of curvature
(b) At the centre of curvature
(c) Beyond the centre of curvature
(d) Between the pole of the mirror and its principal focus.
When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.
Why do stars twinkle?
A bulb is rated at 10 V , 200 m A. Calculate its (i) Power and (ii) resistance.
Two wires of equal length, one of copper and the other of manganin(an alloy) have same resistance. Which one has more thickness?
Compare and contrast bio-mass and hydro electricity as sources of energy.
At noon , the sun appears as white but in morning or evening appears as reddish. Why?
What are the disadvantages of fossil fuels?
State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with a green insulation is usually the live wire of an electric supply.
An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.
What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
An object of size 1 cm is placed on the axis and 15cm from a concave mirror of focal length 10 cm. Find the position , nature and size of the image.
Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?
(a) Geothermal energy 
(b) Wind energy
(c) Nuclear energy 
(d) Bio-mass
Define absolute refractive of a medium.
A concave lens has a focal length of 15 cm . At what distance should the object from the lens be placed so that it forms an image at 10cm from the lens? Also , find the magnification produced by the lens?
When a current I passes through a resistance across which a potential difference exists. Find the rate at which energy is being dissipated?
What is the role of the split ring in an electric motor ?
Explain the underlying principle and working of an electric generator by drawing a labeled diagram. What is the function of brushes?
Why don’t two magnetic lines of force intersect each other?
Why does the sky appear dark instead of blue to an astronaut?
A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R'''', then the ratio R/R'''' is −
(a)  1/25
(b)  1/5
(c) 5
(d) 25
What are the limitations of extracting energy from −
(a) The wind?
(b) Waves? 
(c) Tides?
Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Name a natural phenomenon in which spectrum is formed .
Draw neat diagram to show refraction of a light ray through a prism. Mark angle of incidence, angle of emergence, incident ray, refracted ray and angle of deviation.
Draw a neat and labeled diagram of a human eye. What is the function of retina and write the nature of image formed on the retina.
In series combination of resistances , how does potential difference through individual resistance vary?
Which of the following terms does not represent electrical power in a circuit?
(a) I2R
(b) IR2
(c) VI
(d) V2 / R
The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
Judge the equivalent resistance when the following are connected in parallel:
(a) 1 Ω and 10Ω
1 Ω and 10
Ω and 10Ω
Explain why the planets do not twinkle?
When does an electric short circuit occur?
Draw ray diagram showing the position ,nature and size of the image for object placed
(i) at focus of concave mirror
(ii) at centre of curvature of concave mirror
(iii) In front of convex mirror. 
The phenomenon of electromagnetic induction is
(a) The process of charging a body
(b) The process of generating magnetic field due to a current passing through a coil
(c) Producing induced current in a coil due to relative motion between a magnet and the coil
(d) The process of rotating a coil of an electric motor
Name a device that helps to maintain a potential difference across a conductor.
List the properties of magnetic lines of force.
A 14 year old student is not able to see clearly the questions written on the blackboard placed at a distance of 5 m from him.
(a) Name the defect of vision he is suffering from
(b) With the help of a labeled diagram show how this defect can be corrected.
(c) Name the type of lens used to correct this defect.
How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.
Calculate the wave length of light (i) in air (ii) in glass if the frequency of light is 6 x 1014 Hz. The refractive index of glass is 1.5. 
Name the type of a mirror used in the following situations.
(a) Headlights of a car
(b) Side/rear-view mirror of a vehicle
(c) Solar furnace.
Support your answer with reason.
What do  you mean by refraction of light? State laws of refraction of light. Draw ray diagram to show refraction through a rectangular glass slab?
The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.
An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature and size.
When light undergoes refraction , what happens to its frequency ? How is speed of light affected in vacuum due to change in wavelength of light?
What is the principle of an electric motor?
You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in Table.
In the circuit shown below, calculate
(i) Total resistance
(ii) Total current drawn from the battery and current in each arm.

For what positions of object a concave mirror form
(a) an enlarged and virtual image
(b) a real image of equal size of the object? 
Why is red color selected for danger signal lights?
What are main causes of hypermetropia?
If current passed through a given heating coil is doubled then what will happen to the rate of heat produced ?
What is spectrum?
How has the traditional use of wind and water energy been modified for our convenience?
What determines the rate at which energy is delivered by a current?
Why do the stars twinkle but a planet does not ?
What are the qualities of an ideal source of energy?
What happens to the image distance in the eye when we increase the distance of an object from the eye?
Derive the relation , when resistors are joined is parallel. Draw circuit diagram also.
A normal human eye can not see the objects clearly placed at distances less than 25cm from it. Explain why?
What is presbyopia? How is it corrected?
Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
What precaution should be taken to avoid the overloading of domestic electric circuits?
Name the type of mirror used in following situations (i) Head lights of a car  (ii) rear – view of a vechile.
State two applications of heating effect of current.
What does m = +1 stand for?
A convex mirror used  as rear – view mirror in a car has 4 m radius of curvature. If a Truck located at 6 m from this mirror,“find its position, nature and size of the image.
Which color of light bends most and which least while passing through a prism?
Which light is scattered easily ? To an astronaut why does the sky appear dark instead of blue?
Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be −
(a) 1:2
(b) 2:1
(c) 1:4
(d) 4:1
The least distance of distinct vision for a young adult with normal vision is about
(a) 25 m 
(b) 2.5 cm 
(c) 25 cm 
(d) 2.5 m
What is long sightedness? Describe with the help of ray diagram, how this defect may be corrected by using spectacles. Also draw ray diagram to show hypermetropic eye.
Which source produces alternating current ?
What is a good fuel?
The image of a candle is formed by a convex lens on a screen. The lower half is painted black to make it completely opaque . yet this lens produces a complete image why?
Give the suitable title for the following diagram.
The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the less required to the correct the problem?
Derive relation for equivalent resistance, when R1,Rand R3 are connected in series.
What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
A concave lens of the focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.
A wire is stretched to double of its length. What is the effect on its resistivity?
Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
Name two energy sources that you would consider to be renewable. Give reasons for your choices.
Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)
(a) Mass 
(b) Speed
(c) Velocity
(d) Momentum
For an electric heater of 1000 W rating at 220 V , fuse of how much capacity is to be used ?
What is the cause of dispersion ? Explain.
A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
At the time of short circuit, the current in the circuit
(a) Reduces substantially
(b) Does not change
(c) Increases heavily
(d) Vary continuously
A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?
What is geothermal energy?
For the circuit diagram given below

(i) Effective resistance of the circuit  
(ii) Find current through 6Ω.
(iii) Find P.D across 30Ω.
Name two safety measures commonly used in electric circuits and appliances.
What is meant by saying that the potential difference between two points is 1 V?
Name the part of our eyes that helps us to focus near and distant objects in quick succession.
What is meant by power of accommodation of the eye?
The refractive index of water is 4/3 and out of glass is 3/2 . Calculate the refractive index of glass with respect to water?
Which of the following is not an example of a bio-mass energy source?
(a) Wood     
(b) Gobar gas
(c) Nuclear energy
(d) Coal
Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
How many electrons will constitute one ampere of current through a cross section of conductor?
Why does sun appear oval at sunset and circular at noon?
A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?
A ray of light strikes a mirror at angle of 30o .What is the angle of incidence and reflection?
On what factors does the resistance of a conductor depend?
Draw a diagram to illustrate the recombination of dispersed light by a prism.
Define the unit of current.
The device used for producing electric current is called a
(a) Generator
(b) Galvanometer
(c) Ammeter
(d) Motor
Why does the cord of an electric heater not glow while the heating element does?
Which of the following lenses would you prefer to use while reading small letters found in a dictionary?
(a) A convex lens of focal length 50 cm
(b) A concave lens of focal length 50 cm
(c) A convex lens of focal length 5 cm
(d) A concave lens of focal length 5 cm
If you could use any source of energy for heating your food, which one would you use and why?
Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.
Can absolute refractive index of a medium be less than unity? Can relative refraction index of a medium with respect o another be less than unity?
Why does a compass needle get deflected when brought near a bar magnet?
The change in focal length of an eye lens is caused by the action of the
(a) Pupil
(b) Retina
(c) Ciliary muscles
(d) Iris
Draw the symbols of following electrical components
(a) An electric cell (b) A battery (c) Galvanometer (d) A cell joint (e) Switch closed (f) Variable resistor
Define 1 dioptre of power of a lens.
There are two electric bulbs (i) Marked 100 w, 200 V and (ii) marked 40 w, 200 V. Which one of the two has a higher resistance? Explain.
Can any source of energy be pollution-free? Why or why not?
Define following terms related to spherical mirrors 
(i) pole
(ii) Principal axis 
(ii) Aperture
What is the far point and near point of the human eye with normal vision?
A man cannot see object closer than 100 cm from the eye clearly . what is the power of the corrective lens he should use?
What happens to the image distance in the eye when we increase the distance of an object from the eye?
The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.
What is the composition of eye lens ? State the function of lens. What is the focal length of the eye lens when the ciliary muscles are fully relaxed?
What are the main causes of myopia?
Why does the Sun appear reddish early in the morning?
A ray of light incident on a spherical mirror normally. What is angle of refraction?
What does negative sign of ‘m’ and ‘h’ stand for?
When the light entering the cornea of the eyeball is very bright, how does the iris behave?
Compare and contrast fossil fuels and the Sun as direct sources of energy.
What are the limitations of the energy that can be obtained from the oceans?
A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) Towards south    
(b) Towards east
(c) Downward
(d) Upward
The refractive index of diamond is 2.42. What is the meaning of this statement?
Choose the correct option.
The magnetic field inside a long straight solenoid-carrying current 
(a) Is zero
(b) Decreases as we move towards its end
(c) Increases as we move towards its end
(d) Is the same at all points
Explain different ways to induce current in a coil.
What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire
(b) The field consists of straight lines parallel to the wire
(c) The field consists of radial lines originating from the wire
(d) The field consists of concentric circles centred on the wire
What is the name given to the phenomenon of splitting of whites light into seven colors?
What is the name of a physical quantity which is equal to ?
Which one of the following materials cannot be used to make a lens?
(a) Water
(b) Glass
(c) Plastic
(d) Clay
Draw V-I graph for an ohmic resistor, what does the slope of this graph indicate?
Define electric current and potential difference. Draw a circuit diagram to verify ohm’s law. How many 176Ω resistors (in parallel) are required to carry 5A on a 220 V line?
What is the nature of the image formed at the retina of the eye?
What is the shape of V-I graph for a metallic wire?

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