STD-X, ELECTRICITY, PROBLEMS ON OHM'S LAW

 

1.  Calculate the potential difference required across a conductor of resistance 5 Ω to flow a current of 1.5 A through it.

 

ANS: Given, R = 5 Ω

                       I = 1.5 A

From Ohm’s law, V = IR = 1.5 x 5 = 7.5 V

 

2.  How much electric current is produced on applying p.d of 30 volts on a wire of resistance 20 Ω?

 

ANS: Given, R = 20 Ω

                      V = 30 V

According to Ohm’s law, V=IR

Therefore, I = V/R = 30/20 = 1.5 A

 

3.  If 5 ampere current flowing through a wire, develops a potential difference of 50 volts across its ends, find the resistance of the wire.

 

ANS: Given, I = 5 A

                      V = 50 V

Using Ohm’s law, V = IR

Therefore, R = V/I

                       = 50/5 = 10 Ω

 

4.  The p.d. 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 p.d. is increased to 120 V?

 

( As, current is directly proportional to Potential difference

So, as V is doubled (from 60 V to 120 V), current will also be doubled. So, the answer will be 2 x 4 = 8 A)

ANS: Given, V = 60 V

                       I = 4 A

According to Ohm’s law, V = IR

                                 So, R = V/I = 60/4 = 15 Ω

When the potential is increased to 120 V, the current is given by,

                                       I = V/R = 120/15 = 8 A

The current through the heater becomes 8 A.

 

5.  A relay with a resistance of 12 Ω is in an electric circuit with one side at a potential of 85 volts and the other at 71 volts. How much current is in the relay?

 

ANS: The p.d. across the relay = V₂ – V₁ = 85 V – 71 V =  14 V

Therefore, the current in the relay, I = V/ R = 14/12 = 1.2 A

PROBLEMS FOR PRACTICE

6.  A lamp of resistance 80 Ω draw a current of 0.75 A. Find the line voltage.

7.  An electric heater draw a current of 5 A when connected to 220 V mains. Calculate the resistance of its filament.

8.  How much current will an electric heater draw from a 200 V source, if the resistance of the filament is 100 Ω?

9.  How much current does an electric heater draw from a 220 V line, if the resistance of the heater (when hot) is 50 Ω?

10.  A bulb when cold has 1 Ω resistance. It draws a current of 0.3 A when glowing from a source of 3 V. Calculate the resistance of the bulb when it is glowing and explain the reason for the difference in resistance.

STD-X, HUMAN EYE AND THE COLOURFUL WORLD- Scattering of Light, Most important MCQs

 

1.  The scattering of light by colloidal solution is called-

(a) Tyndall effect

(b) Raman effect

(c) Colloidal effect

(d) Refraction effect

 

ANS: Tyndall effect

 

2.  Which phenomenon is responsible for making the path of light visible?

(a) Tyndall effect

(b) Total internal refraction effect

(c) Colloidal effect

(d) Refraction effect

 

ANS: Tyndall effect

 

3.  Which of the following is not an example of Tyndall effect?

(a) When a fine beam of light enters a smoke filled dark room through a small hole

(b) Twinkling of stars

(c) When sunlight passes through a canopy of dense forest in misty conditions.

(d) Shinning a beam of flashlight into the glass of milk

 

ANS: Twinkling of stars

 

4.  The colour of the scattered light depends on ____ of the scattering particles.

(a) colour

(b) speed

(c) size

(d) number

 

ANS: size

 

5.  Fine particles mostly scatter ______.

(a) shorter wavelength such as blue

(b) longer wavelength such as blue

(c) shorter wavelength such as red

(d) longer wavelength such as red

 

ANS: shorter wavelength such as blue

 

6.  Large size particles mostly scatter-

(a) shorter wavelength such as blue

(b) longer wavelength such as blue

(c) shorter wavelength such as red

(d) longer wavelength such as red

 

ANS: longer wavelength such as red

 

7.  The main reason behind the phenomenon of scattering of light is,

(a) light has large wavelength value of the order of few metres

(b) light wave can travel through vacuum

(c) light waves are deflected by fine particles, molecules present in the air

(d) Sun light is composite light with blue as its major constituent

 

ANS: Light waves are deflected by fine particles, molecules present in the air

 

8.  If size of particles is comparable to wavelengths of incident light then,

(a) scattering does not take place

(b) all wavelengths will get scattered equally

(c) scattered light appears violet

(d) internal reflection takes place

 

ANS: all wavelengths will get scattered equally

 

STD-X, ATMOSPHERIC REFRACTION: Twinkling of Stars, Advanced Sunrise and Sunset, Most important MCQs

 1.  The air layer of atmosphere whose temperature is less then the hot layer behave as optically,

(a) denser medium
(b) rarer medium
(c) inactive medium
(d) either denser or rarer medium

 

ANS: denser medium

 

2.  Refraction of light by the earth’s atmosphere due to variation in air density is called
(a) atmospheric reflection
(b) atmospheric dispersion
(c) atmospheric scattering
(d) atmospheric refraction

ANS: atmospheric refraction

 

3. The word optical density of atmosphere refers to- 

(a) thickness of atmosphere

(b) brightness of atmosphere

(c) degree to which atmosphere reduces intensity of light passing through it

(d) degree to which atmosphere focuses light

 

ANS: degree to which atmosphere reduces intensity of light passing through it.

 

4.  Twinkling of stars is due to atmospheric

(a) dispersion of light by water droplets

(b) atmospheric refraction of light by different layers of varying refractive indices

(c) scattering of light by dust particles

(d) internal reflection of light by clouds.

 

ANS: atmospheric refraction of light by different layers of varying refractive indices

 

5.  As light from a far off star come down towards the earth

(a) it bends away from the normal

(b) it bends towards the normal

(c) it does not bend at all

(d) it reflects back

 

ANS: it bends towards the normal

 

6.  The stars appear shifted from their actual position due to the phenomenon of,

(a) diffraction of light

(b) scattering of light

(c) refraction of light

(d) internal reflection of light

 

ANS: refraction of light

 

7. The stars twinkle but the planets do not twinkle at night because-

(a) the stars are big but the planets are smaller

(b) the stars are very much nearer but planets are far off

(c) the stars are far off but planets are nearer to the earth

(d) planets produce light which is reflected by stars

 

ANS: the stars are far off but planets are nearer to the earth

 

8.  The planets do not twinkle because-

(a) atmospheric refraction does not take place

(b) planets are equivalent to a point source

(c) planets are equivalent to an extended source

(d) planets do not have atmosphere

 

ANS: planets are equivalent to an extended source

 

9. Advanced sunrise and delayed sunset are explained on the basis of 

(a) dispersion of light

(b) scattering of light

(c) Tyndall effect

(d) atmospheric refraction

 

ANS: atmospheric refraction

 

10. The Sun is visible before the sunrise and after the sunset because of the phenomenon of ______.  

(a) reflection

(b) refraction

(c) dispersion

(d) polarization

 

ANS: refraction

 

STD-X, HUMAN EYE AND THE COLOURFUL WORLD: Dispersion, MOST IMPORTANT MCQs

1. Which of the following statements is correct regarding the propagation of light of different colours of white light in air?
(a) Red light moves fastest.
(b) Blue light moves faster than green light.
(c) All the colours of the white light move with the same speed.
(d) Yellow light moves with the mean speed as that of the red and the violet light

ANS: All the colours of the white light move with the same speed

 

2.  The splitting of light into its component colours is called-
(a) Spectrum
(b) Dispersion
(c) Tyndall effect
(d) Refraction

 

ANS: Dispersion

 

3.  Dispersion is caused due to _____ of light.

(a) reflection

(b) refraction

(c) scattering

(d) reflection and refraction

 

ANS: refraction

 

4.  The dispersive power of prism depends upon-
(a) The shape of the prism
(b) The material of the prism
(c) The angle of the prism
(d) Height of the prism

 

ANS: the material of the prism

 

5.  The dispersive power will be maximum for-
(a) Flint glass (n=1.65)
(b) Crown glass (n=1.51)
(c) Mixture of glass
(d) None of these

 

ANS: Flint glass

 6.  Sumitra was given two glass prisms. One was made of ordinary glass and other one was of flint glass (Given that refractive index of flint glass is more than that of ordinary glass). She traced the path of rays through both and after observing the diagram and concluded that bending of light for given angle of incidence was

(a) more in the prism made of flint glass

(b) more in the prism made of ordinary glass

(c) same in both the glass prisms

(d) independent of the nature of glass of which the prism was made

 

ANS: more in the prism made of flint glass

6.  Sumitra was given two glass prisms. One was made of ordinary glass and other one was of flint glass (Given that refractive index of flint glass is more than that of ordinary glass). She traced the path of rays through both and after observing the diagram and concluded that bending of light for given angle of incidence was

(a) more in the prism made of flint glass

(b) more in the prism made of ordinary glass

(c) same in both the glass prisms

(d) independent of the nature of glass of which the prism was made

 

ANS: more in the prism made of flint glass

 

7.  For a light travelling in a prism choose the correct option. Inside the prism,

(a) all the colours have same angle of refraction

(b) the colour with more deviation has lesser refractive index

(c) the colour with lesser deviation has more speed

(d) all the colours travel with same speed

 

ANS: the colour with lesser deviation has more speed

 

8.  Which of the colours of visible light has maximum wavelength?
(a) Yellow
(b) Red

(c) Violet

(d) Green

 

ANS: Red

 

STD-X, HUMAN EYE AND THE COLOURFUL WORLD, Important Questions on Glass Prism, MCQs

1.  A glass prism has-

(a) 5 rectangular surfaces

(b) 4 rectangular surfaces

(c) 2 triangular bases and 3 rectangular surfaces

(d) 2 rectangular surfaces and 3 triangular bases

 

ANS: 2 triangular bases and 3 rectangular surfaces

 

2.  A prism is used to-

(a) pass the light undeviated

(b) deviate a light path by reflection only

(c) refract, reflect or diffract the light depending on experimental condition

(d) deviate a light path by refraction

 

ANS: deviate a light path by refraction

 

3.  The angle between two lateral surfaces of a prism is called as

(a) angle of prism

(b) angle of refraction

(c) reflecting index of the prism

(d) dispersion angle

 

ANS: angle of prism

 

4.  The angle between two plane rectangular refracting surfaces of a prism is called as

(a) refracting angle of the prism

(b) angle of refraction

(c) reflecting angle of the prism

(d) dispersion angle

 

ANS: refracting angle of the prism

 

5.  The angle between the directions of the incident ray and the emergent ray is called-

(a) angle of deviation

(b) angle of refraction

(c) reflecting angle of the prism

(d) dispersion angle

 

ANS: angle of deviation

 

6.  For an equilateral prism the angle of the prism is-

(a) 60⁰

(b) 45⁰

(c) 90⁰

(d) 30⁰

 

ANS: 60⁰

 

7.  How many times refraction occurs when a ray passes through a prism?

(a) 1

(b) 4

(c) 3

(d) 2

 

ANS: 2