Question Bank - Magnetic effects of electric current

1.    Why does a compass needle got deflected when brought near a bar magnet?

2.    Draw magnetic field lines of a bar magnet.

3.    List any two properties of magnetic field lines.

4.    The magnetic field in a given region is uniform. Draw a diagram to represent it.

5.    Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right hand rule to find out the direction of magnetic field inside and outside the loop.

6.    Why don’t two magnetic field lines intersect each other?

7.    Explain different ways to induce current in a coil.

8.    State Fleming’s left hand rule.

9.     What is the principle of electric motor?

10.   State the principle of electric generator.

11.   State Fleming’s right hand rule.

12.   State right hand thumb rule.

13.   Name some sources of direct current.

14.   Which sources produces alternating current?

15.   Name two safety measures commonly used in electric circuit and appliances.

16.   What precautions should be taken to avoid the overloading of domestic electric circuit?

17.   An electric oven of a 2kW power rating is operated in a domestic circuit (220 V) that has a current rating of 5A. What result do you expect? Explain.

18.   Define electromagnetic induction.

19.   List three sources of magnetic field.

20.   How does a solenoid behaves like a bar magnet? Can you determine the north and south poles of a current carrying solenoid with the help of a bar magnet? Explain.

21.   When is the force experienced by a current-carrying conductor placed in a magnetic field largest?

22.   Imagine you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?

23.   A coil of insulated copper wire is connected to a galvanometer. What would happen if a bar magnet is

  (i) Pushed into the coil.

  (ii) Withdrawn from inside the coil.

  (iii) Held stationary inside the coil.

24.   Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.

25.   State the rule to determine the direction of a

  (i) Magnetic field produced around a straight conductor carrying current.

  (ii) Force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.

  (iii) Current induced in a coil due to its rotation in a magnetic field.

26.   When does an electric short-circuit occur?

27.   What is the function of an earth wire? Why is it necessary to earth metallic appliances?

28.   What is the effect of inserting a soft iron core inside a current-carrying solenoid? What is this arrangement known as?

29.   What is the capacity of an electric fuse used in (i)lighting circuit (ii) power circuit used in household supply?

30.   State two characteristics of electric fuse wire.

31.   State two ways by which the strength of an electromagnet can be increased.

32.   State three factors on which the magnitude of force on a current carrying –conductor placed in a magnetic field depends. Can this force be zero for some position of the conductor?

33.   Draw the magnetic field lines around a straight conductor carrying current.

34.   Draw the magnetic field lines due to a current-carrying circular wire.

35.   What is solenoid? Draw the magnetic field lines due to a current carrying solenoid.

36.   Compare the magnetic field produced by a bar magnet and a solenoid?

37.   What is the difference between a direction current and an alternating current? How many times does AC used in India change direction in one second?

38.   In what way can the magnitude of induced current be increased?

39.   How does AC differ from DC? What are the advantages and disadvantages of AC over DC?

40.   What is earthing? How does it work as a safety measure?

41.   What is the function of earth wire? Why is it necessary to earth the metallic appliances?

42.   What is the role of fuse used in series with any electrical appliance?

43.   Why should a fuse with defined rating not be replaced by one with a larger rating?

44.   How is the direction of magnetic field at a point determined?

45.   What is the direction of magnetic field at the centre of a current-carrying circular loop?

46.   A magnetic compass shows a deflection when placed near a current carrying wire. How will the deflection of the compass get affected if the cyrrent in the wire is increased? Support your answer with reason.

47.   What does the divergence of magnetic fied lines near the ends of a current carrying straight solenoid indicate?

48.   An electron enters a uniform magnetic field at right anges to it as shown in the figure. In which direction will this electron move? State the principle applied by you in finding the direction of motion of the electron?

49.   What is an electric fuse? How does it function?

50.   A fuse is rated at 8 A, it means:

   (a) It will not work if current is less than 8 A.

   (b) It has a resistance of 8 ohm.

   (c) It will work only if current is 8 A.

   (d) It will burn if current exceeds 8 A.

Question Bank Electricity

A Question Bank provides you a plenty of good questions for practice and meaningful discussion with your peers. It saves time and make you confident in the subject. The following is the Question Bank on Electricity Class 10 standard.

1.    What does an electric circuit mean?

2.    Define the unit of current.

3.    Calculate the number of electrons constituting one coulomb of charge.

4.    A current of 0.5 A is drawn by a filament of an electric bulb for 10 minutes. Find the amount of charge that flows through the circuit. (Ans. 300 C)

5.    Name the instrument used to measure electric current in a circuit. How is this instrument connected in a circuit? Draw a simple circuit diagram to explain your answer.

6.    Which particles constitute electric current in a metallic conductor?

7.    Name two units for expressing the small values of current. Also write their symbols. How are these units related to ampere?

8.    Name a device that helps to maintain potential difference across a conductor.

9.    What is meant by saying that potential difference between two points is 1V?

10.   Write the relation which states the relation between potential difference and work done.

11.   How much energy is given to each coulomb of charge passing through a 6V battery?

12.   How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V?

13.   Name the device that measures the potential difference across two points in an electric circuit. How it is connected in an electric circuit?

14.   Name and state the law which relates the current in a conductor to the potential difference across a conductor and the current flowing through it.

15.   Define the SI unit of resistance.

16.   (a) How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 Ω? (Ans. 0.183 A)

        (b) How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100 Ω? (Ans. 2.2 A)

17.   The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 V? (Ans. 8 A)

18.   A wire of given material having length l and area of cross-section A has a resistance of 4 Ω. What would be the resistance of another wire of the same material having length l/2 and area of cross-section 2A? (Ans. 1 Ω)

19.   On what factors does the resistance of a conductor depend?

20.   Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?

21.   Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?

22.   Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?

23.   When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor. (Ans. 4800Ω)

24.   Why is the tungsten used almost exclusively for filament of electric lamps?

25.   Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?

26.   How does the resistance of a wire vary with its area of cross-section?

27.   Why copper and aluminium wires are usually employed for electricity transmission?

28.   Keeping the potential difference constant, the resistance of a circuit is doubled. By how much does the current change?

29.   Give two examples of materials which are (i) good conductor (ii) resistor (iii) insulator (iv) poor conductor.

30.   Why do electricians wear rubber hand-gloves while working with electricity?

31.   Name the device used to change resistance in a circuit to regulate current without changing the voltage source.

32.   What is nichrome? State its one property and one use.

33.   Define resistivity. What is its SI unit? On what factor does it depends?

34.   A wire of resistance 20 Ω is stretched to double its length. What will be its new (i) resistivity (ii) resistance? (Ans. New R = 80 Ω)

35.   The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below –

                    I (amperes)    0.5     1.0      2.0      3.0      4.0


                    V (volts)       1.6       3.4      6.7     10.2     13.2

Plot a graph between V and I and calculate the resistance of that resistor.

36.   Write the use of following components in an electric circuit
        (a) Cell/battery
        (b) Ammeter
        (c) Connecting wires
        (d) Switch/plug key

37.   A wire of resistance R is cut into five equal pieces. These five pieces of wire are then connected in parallel. If the resultant resistance of this combination be R then the ratio of resultant to the original will be?

38.   A radio set draws a current of 0.36 A for 15 minutes. Calculate the amount of electric charge that flows through the circuit. (Ans. 324 C)

39.   Potential difference between two points of a wire carrying 2 ampere current is 0.1 volt. Calculate the resistance between these points. (Ans. 0.05Ω)

40.   A simple electric circuit has a 24 V battery and a resistor of 60 ohms. What will be the current in the circuit? The resistance of the connecting wires is negligible. (Ans. 0.4 Ω)

41.   Find resistance between A and B in following network

42.   A resistance of 6 ohms is connected in series with another resistance of 4 ohms. A potential difference of 20 volts is applied across the combination. Calculate the current through the circuit and potential difference across the 6 ohm resistance. (Ans. 2 A, 12 V)

43.   Calculate the work done in moving a charge of 5 Coulombs from a point at a potential of 210 Volts to another point at 240 Volts. (Ans. 150 J)

44.   How many electrons pass through a lamp in one minute if the current be 200 mA? (72 x 10^18)

45.   Calculate the current supplied by a cell if the amount of charge passing through the cell in 4 seconds is 12 C ? (Ans. 4 A)

46.   A 2 Volt cell is connected to a 1 Ω resistor. How many electrons come out of the negative terminal of the cell in 2 minutes? (Ans. 1440 x 10^18)

47.   A torch bulb when cold has 1Ω resistance. It draws a current of 0.3 Ampere when glowing from a source of 3 V. Calculate the resistance of the bulb when glowing and explain the reason for the difference in resistance. (Ans. 10Ω)

48.   A current of 0.2 Ampere flows through a conductor of resistance 4.5 Ω. Calculate the potential difference at the ends of the conductor. (Ans. 0.9 V)

49.   You have two metallic wires of resistances 6 ohm and 3 ohm. How will you connect these wires to get the effective resistance of 2 ohm?

50.   State Ohm’s law. “The resistance of a conductor is 1Ω.” What is meant by this statement?

51.   Prove that 1 J is equivalent to 1 Vx A x s.

52.   How long does it take a current of 5.0 mA to deliver 15 C of charge? (Ans. 3000 s)

53.   What is the potential difference between two points if 1.0 kJ of work is required to move 0.5 C of charge between the two points? (Ans. 2000 V)

54.   What is the voltage of a source which provides 12.0 J to each Coulomb of charge present?

55.   What is the potential difference between two points when a charge of 80.0 C has 4.0 x 10^3J of energy supplied to it as it moves between the two points? (Ans. 50 V)

56.   There is a current of 0.50 A through an incandescent lamp for 5.0 min, with a voltage of 115 V. How much energy does the current transfer to the lamp? What is the power rating of the lamp? (Ans. 17250 J, 57.5 W)

57.   If there is a current of 2.0 A through a hair dryer transferring 11 kJ of energy in 55 s, what is the potential difference across the dryer? (Ans. 100 V)

58.   An electric drill operates at a potential difference of 120V and draws a current of 6.0 mA. If it takes 40 s for the drill to make a hole in a piece of wood, how much energy is used by the drill? (Ans. 28.8 J)

59.   An electric toaster operating at a potential difference of 115 V uses 3220 J of energy during the 20 sec it is on. What is the current through the toaster? (Ans. 1.4 A)

60.   A motor draws a current of 2.0 A for 20.0 sec in order to lift a small mass of 500 g. If the motor does a total of 9.6 kJ of work calculate the voltage drop across the motor. (Ans. 240 V)

61.   In a lightning discharge, 30.0 C of charge moves through a potential difference 108 V in 20 minute. Calculate the current of the lightning bolt. (Ans. 0.025 A)

62.   How much energy is gained by an electron accelerated through a potential difference of 3.0 x 10^2 V? (4.8 x 10­-17 J)

63.   A 12V car battery can provide 6 A for 1.0 h. how much energy is stored in the battery? (Ans. 259200 J)

64.   a) Describe the difference between current in a series circuit and current in a parallel circuit.
        b) Describe the difference between voltage in a series circuit and voltage in a parallel circuit.

65.   Draw a schematic diagram of the following circuit: One power source and a resistor are connected in series with a combination of 3 light bulbs connected in parallel with each other. Include a fuse, 4 switches, a voltmeter, and an ammeter. The fuse should protect the whole circuit, one switch should shut off the whole circuit and the other switches should control the individual bulbs. The ammeter should read current drawn from power source and the voltmeter the voltage of the resistor.

66.   Describe the effect on the rest of the bulbs in the above problem when one burns out. Will the remainder glow brighter or dimmer? What will be the effect on the source?

67.   a) What is a short circuit? b) Why is it dangerous? c) Give two ways to protect against short circuits.

68.   A conductor has a length of 2.0 m and a radius of 3.0 mm. If the resistance is R = 100 Ω, calculate the new resistance if the same material has:
        a) length = 6.0 m and r = 6.0 mm (Ans. 75 Ω)
        b) length = 1.0 m and r = 1.0 mm (Ans. 450 Ω)

69.   List two ways to increase the current drawn by a circuit.

70.   A voltmeter measures a voltage drop of 60.0 V across a heating element while an ammeter reads the current through it as 2.0 A. What is the resistance of the heating coil? (Ans. 30Ω)

71.   How much current flows through a 7.5 W light bulb with a potential difference of 1.5 V? (Ans. 5A)

72.   A set of 6 identical motors are connected in series to a 120 V source drawing 1.0 A of current. Find:
       a) R total
       b) R of each motor
       c) Voltage drop across each load. (Ans. 120Ω, 20Ω and 20 V)

73.   A set of 6 identical motors are connected in parallel to a 150 V source drawing 1.2 A of current. Find:
        a) R total
        b) R of each motor
        c) Current through each motor
        d) Voltage drop across each load. (Ans. 125Ω, 750Ω, 0.2 A and 150 V)

74.   Do resistors in parallel increase or decrease total resistance?

75.   What resistance must be added in series to a circuit containing a 45 ohm resistor in order to draw 2.0 A of current from a 120V source? (Ans. 15 Ω)

76.   What makes the electric charge to flow?

77.   The V–I graph is a straight line that passes through the origin of the graph. What do you conclude from this observation?

78.   Define the commercial unit of energy. Relate it to joules.

79.   Discuss the activity to show that resistance of a conductor depends on its length and area of cross section.

80.   Which common factor affects both resistance as well as resistivity?

81.   Alloys are commonly used in electrical heating devices. Why?

82.   It is impracticable to connect an electric bulb and an electric heater in series. Why?

83.   What is heating effect of electric current? Name the various devices in which this effect is utilized.

84.   State the Joule’s law of heating. Derive the expression for the same.

85.   Which effect of current is responsible for the glow of an electric bulb? Explain.

86.   The bulbs are usually filled with few gases. Name those gases. Also discuss the cause for the same.

87.   Which metal is used as the filament of an electric bulb and why?

88.   How does a fuse work in the electric circuit?

89.   Which materials are preferred for a fuse wire and why?

90.   Give the ratings of various fuses used in the domestic circuit.

91.   A torch bulb is rated at 3V and 600mA. Calculate it’s a) Power b) Resistance c) Energy consumed if it is lighted for 4 Hrs. (Ans. 1.8 W, 5 Ω, 0.0072kWh/25920 J)

92.   Which will offer more resistance a 50W lamp or 25W lamp bulb and how many times? (ans. 25 W, 2 times)

93.   Why should the heating element of an electric iron be made of iron, silver or Nichrome wire?

94.   If a wire is stretched to triple its original length, what happens to its resistivity?

95.   Two identical resistors each of resistance 10 ohm are connected 1) in series 2) in parallel, in line to a battery of 6volts. Calculate the ratio of power consumed in the combination of resistors in the two cases. (Ans. 1:4)

96. A bulb is rated at 220V- 100W. What is its resistance? Five such bulbs burn for 4 hrs. What is the energy consumed? Calculate the cost if the rate is Rs. 5 per unit? (Ans. 484 Ω 2kWh, Rs 10)

97.   Two lamps rated 100W, 220V and 120W, 220V are connected in parallel to 220V supply. Calculate the total current through the circuit. (Ans. 1 A)

98.   How does the resistance of wire change when 1) Its length is doubled 2) Area is doubled?

99.   A wire of resistance 10ohm is bent in the form of a closed circle. What is the effective resistance between the two points at the end of any diameter of the circle? (Ans. 2.5 Ω)

100.  When resistances are connected in series, which physical quantity remains constant?

101.  When resistances are connected in parallel, which physical quantity remains constant?

102.  Resistance of an incandescent filament of lamp is more than that when it is at the room temperature. Why?

103.  The length of a wire is doubled and its cross sectional area is also doubled. What is the change in its (i) resistivity (ii) resistance?

104.  Name two characteristics of a heating element wire.

105.  For an electric iron of 1kW rating at 220V, fuse of how much capacity is to be used? (Ans. 5A)

106.  What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?

107.  How can three resistors of resistances 2Ω, 3Ω and 6Ω be connected to give a total resistance of (a) 4Ω (b) 1Ω ?

108.  Why does the cord of an electric heater not glow while the heating element does?

109.  Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50V. (Ans. 4800 kJ)

110.  An electric iron of resistance 20 Ω takes a current of 5A. Calculate the heat developed in 30 s. (Ans. 15 kJ)

111.  What determines the rate at which energy is delivered by current?

112.  An electric motor takes 5A from a 220 V line. Determine the power of the motor and the energy consumed in 2 hours. (Ans. 1.1 kW, 2.2 kWh)

113.  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 obtain the ratio of .

114.  An electric bulb is rated 220 V and 100 W. What will be the power consumed when it is operated on 110 V ? (Ans. 25 W)

115.

V-I graph for two conductors A and B obeying Ohm’s law is given in figure 4. Which conductor has more resistance?

116.

V-I graph for parallel and series combination of two metallic resistors is shown as in figure 5. Which graph represents the parallel combination? Justify your answer.

117.  Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then connected in parallel in a circuit across the same potential difference. Obtain the ratio of heat produced in series and parallel combination. (Ans. 1:4)

118.  How many 176 Ω resistors in parallel are required to carry 5 A on a 220 V line? (Ans.4 resistors)

119.  Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A? (Ans. 110 bulbs)

120.  Compare the power used in the 2Ω resistor in each of the following circuits:
        (i) a 6 V battery in series with 1Ω and 2Ω resistors, and
        (ii) a 6 V battery in parallel with 12 Ω and 2Ω resistors. (Ans. 8W, 18 W)

121.  Which uses more energy, a 250 W TV set in 1 hour, or a 1200 W toaster in 10 minutes?

122.  An electric heater of resistance 8Ω draws 15 A from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater. (Ans. 1800 W)

123.  (i) State the formula showing how the current I in a conductor varies when the potential difference V applied across it is increased stepwise.
        (ii) Show this relationship on a schematic graph.
        (iii) Calculate the resistance of a conductor if the current flowing it is 0.2 A, when the applied potential difference is 0.8V.

124.  A torch bulb is rated 2.5 V and 750 mA. Calculate 
         (i) its power, 
         (ii) its resistance, and 
         (iii) the energy consumed if this bulb is lighted for 4 hours.                                                 (Ans. 1.875 W, 3.3Ω, 0.0075kWh)

125.  A wire of resistance 4Ω is doubled on it. Calculate the new resistance of the wire. (Ans. 1Ω)


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SPHERICAL MIRRORS

A mirror whose reflecting surface is a part of an imaginary hollow sphere is known as a spherical mirror.

Spherical mirrors are of two types:

(1) Concave mirrors

(2) Convex mirrors

Concave mirror: It is a spherical mirror whose reflecting surface is towards the centre of the imaginary sphere of which the mirror is a part.

Convex mirror: It is a spherical mirror whose reflecting surface is away from the centre of the imaginary sphere of which the mirror is a part.

Example: The inner shining surface of a steel spoon serves as a concave mirror and the outer shining surface of the steel spoon serves as a convex mirror.

ACTIVITY 1

(1)    Take a large shining spoon. Try to view your face in the inner shining surface of the spoon.

(2)    Bring the spoon close to your face. Observe the image.

(3)    Now move the spoon away from you. Observe the image.

(4)    Now try to view your face in the outer shining surface of the spoon.

(5)    Bring the spoon close to your face. Observe the image.

(6)    Now move the spoon away from you. Observe the image.

Terms related to spherical mirror

(1) Centre of curvature (C)

The centre of curvature of a spherical mirror is the centre of the imaginary hollow sphere of which the spherical mirror is a part.  It is denoted by C.

The centre of curvature is not a part of the spherical mirror. The centre of curvature of a concave mirror lies in front of the spherical mirror and centre of curvature of a convex mirror lies at the back of the mirror.

(2) Pole (P)

The pole of a spherical mirror is the centre of reflecting surface of the mirror. It is denoted by the point P

(3) Radius of curvature (R)

The radius of curvature of a spherical mirror is the radius of the imaginary hollow sphere of which the spherical mirror is a part. It is denoted by R

(4) Principal axis

The principal axis of a spherical mirror is the straight line passing through the centre of curvature C and pole P of the spherical mirror, produced on both sides.

(5) Aperture

The aperture of a spherical mirror is the diameter of the reflecting surface of the mirror

(6) Principal focus of a concave mirror (F)

The principal focus of a concave mirror is a point on the principal axis at which the incident rays parallel to the principal axis after reflection from the concave mirror actually meet at a point on the principal axis.  It is denoted by the letter F

(7) Principal focus of a convex mirror (F)

The principal focus of a convex mirror is a point on the principal axis at which the incident rays parallel to the principal axis after reflection from the convex mirror appears to meet at a point (or appears to diverge from a point)  on the principal axis.  It is denoted by the letter F

(8) Focal Length (f)

It is the distance between the principal focus (F) and pole P of the mirror. It is denoted by letter f.

Relation between focal length (f) and radius of curvature

Provided the aperture of a spherical mirror is much smaller than the radius of curvature, the focal length f can be related to radius of curvature R as

REFLECTION OF LIGHT BY A PLANE MIRROR

Image formed by a point object

Image formed by a finite object

Following are the important characteristics of images formed by a plane mirrors:

(1)  The image formed is always virtual. Such a image cannot be taken on a screen.

(2)  The image formed is always erect.

(3) The size of the image is same as the size of the object.

(4)  The image formed in a plane mirror as far behind the mirror, as the object is in front of the mirror.

(5) The image formed in a plane mirror is laterally inverted i.e. the left side of the object becomes the right side of the image and vice-versa.

LAWS OF REFLECTION OF LIGHT

First Law: The incident ray, the reflected ray and the normal at the point of incidence, all lie in the same plane.

Second Law: The angle of reflection (r) is equal to the angle of incidence (i).

These laws of reflection are valid for all types of reflecting surfaces. The surface may be smooth or rough. It may be a plane mirror, curved mirror, cylindrical or spherical mirror. The surface may be a spoon or a wall or a book. These laws of reflection are valid for all types of surfaces.

When light falls on smooth surfaces, regular reflection will occur. This type of reflection gives rise to image formation.

When light falls on rough surfaces, irregular reflection will occur. This type of reflection gives rise to scattering of light. Such a surface can be seen from all possible directions.

REFLECTION OF LIGHT

When light travelling in a given medium strikes any surface, a part of the incident light bounces back into the same medium. This phenomenon is called reflection.

Light reflected from a surface

Thus in reflection, the path of light rays changes its direction without any change in the medium of light.

Reflection is of two types:

Regular reflection

When the reflecting surface is smooth and well polished, the parallel rays of light incident on it are reflected parallel in one particular direction. This is known as regular reflection.

The regular reflection gives rise to image formation.

Regular reflection

Irregular reflection

When is reflecting surface is rough, the parallel rays falling on it are reflected in different directions. Such a reflection is known as irregular reflection or diffused reflection. No clear image is formed in case of irregular reflection.

Diffused or irregular reflection

Nature of Light

NATURE OF LIGHT

When we switch on a bulb/tube light, everything in the room becomes visible. When we switch off the bulb/tube light nothing can be seen. So we may conclude that it is the light which makes things visible when it falls on objects.

During the day, it is sunlight which makes things visible to us. The sunlight falling on objects is reflected or scattered and this reflected or scattered light when enter our eyes enable us to see those objects.

Thus,

Light is a form of energy which produces in us the sensation of sight.

What actually is light? or What is it made up of?
It is really a mysterious topic. It is an old topic of debate among scientists and science students. The explanation given by scientists appears to be against our common sense or the way we perceives the world. The theories are mind boggling for a student at the secondary level.

In junior classes, our teachers taught that light is a form of a ray which travels in straight line. A combination of rays forms a beam. A ray falling on a mirror is reflected in such a way that angle of incidence and angle of reflection both are equal. The concept of reflection and refraction can be explained completely on the ray theory of light. 

Interference and diffraction are the characteristics of a wave. It is observed that light also undergoes interference and diffraction supporting that light is also a wave. Scientists also explained reflection and refraction on the basis of wave theory. 

Scientists also found some phenomenon which cannot be explained on the basis of wave theory such as photoelectric effect and compton effect. Several experiments conducted on light proves that light is composed of particles known as photon. 

Now this is very confusing whether to call a light a wave or particle.  It is safer to assume that light has a dual character. It behaves like a wave as well as particle.


Properties of light 
(1)    Light travels in a straight line. This property of light is known as rectilinear propagation of light. This straight line path is usually indicated as a ray of light.
(2)   Nothing can travel faster than light. In vacuum the speed of light is 3 x 10⁸ m/s.
(3)  The speed of light in different medium is different. For example, speed of light in glass is 2 x 10⁸ m/s.
(4)   On entering from one transparent medium (say air) to another (say water) light changes its direction. The extent and way of bending depends upon the optical density of two media.
(5)   According to the modern theory of light, Light has a dual character. It is emitted or absorbed as a particle (called photon), but it propagates as a wave.
(6)     The particle character of light is called PHOTON. When light propagates in the form of wave it consist of electric and magnetic field hence light is also known as an electromagnetic wave.

Phenomena related to light:

(1)    Reflection of light
(2)    Refraction of light
(3)    Dispersion
(4)    Scattering
(5)    Interference
(6)    Difraction
(7)    Polarisation
(8)    Doppler effect