Physics MCQs Test P 13

Ray Optics

1. What is the distance between two convex lenses LA and LB with focal lengths FA and FB?

1. FA+FB
2. FA-FB
3. FA
4. FB

Answer: (a) FA+FB

2. If a medium has a critical angle for total internal reflection from the medium to vacuum as 300, what is the velocity of light in the medium?

1. 0.5 × 108 m/s
2. 3 × 108 m/s
3. 1.5 × 108 m/s
4. 0.2 × 108 m/s

Answer: (c) 1.5 × 108 m/s

3. The combination of which of the following processes results in the formation of a rainbow?

1. Dispersion and Total Internal Reflection
2. Dispersion and Absorption
3. Refraction and Scattering
4. Dispersion and Focussing

Answer: (a) Dispersion and Total Internal Reflection

4. What is the focal length of a double concave lens with a radius of curvature 20 cm, if the refractive index of the glass with respect to the air is 5/3?

1. 20 cm
2. -20 cm
3. 15 cm
4. -15 cm

Answer: (d) -15 cm

5. A diverging lens of power 65 D is combined with a convex lens of focal length, f = 20 cm. What are the power and focal length of the combination?

1. 5 D, 33.7 cm
2. 5 D, 66.7 cm
3. 1.5 D, 33.7 cm
4. -1.5 D, 66.7 cm

Answer: (b) 5 D, 66.7 cm

6. When a thin convex lens of glass 5D is immersed in a liquid, it behaves as a divergent lens of focal length 100 cm. What is the refractive index of the liquid?

1. ⅓
2. ⅔
3. ⅗
4. 5/3

Answer: (d) 5/3

7. The magnifying power of an astronomical telescope in normal adjustment is 100. What is the focal length of the objectives and eyepiece of the distance between them is 101 cm?

1. 1 cm and 10 cm respectively
2. 1 cm and 100 cm respectively
3. 10 cm and 1 cm respectively
4. 100 cm and 1 cm respectively

Answer: (d) 100 cm and 1 cm respectively

8. If an equiconvex lens of focal length f and power P is cut into half in thickness, what is the focal length and power of each half?

1. Zero
2. f/2
3. f
4. 2f

Answer: (d) 2f

9. A prism has an angle 600 and refractive index √2, what is the angle of minimum deviation?

1. 900
2. 600
3. 450
4. 300

Answer: (d) 300

10. What is the correct relationship between refractive indices n,n1 and n2 if the behaviour of light is as shown in the figure?

1. n1>n
2. n1<n
3. n1=n
4. None of the above

Answer: (b) n1<n

surface tension

Q1: When there are no external forces, the shape of a liquid drop is determined by

1. Surface Tension of the liquid
2. The density of the liquid
3. The viscosity of the liquid
4. The temperature of air only

Answer: (a) Surface Tension of the liquid

Q2: If T is the surface tension of the soap solution, the amount of work done in blowing a soap bubble from diameter D to a diameter 2D is

1. 2πD2T
2. 4πD2T
3. 6πD2T
4. 8πD2T

Answer: (c) 6πD2T

Q3: If the surface of a liquid is plane, then the angle of contact of the liquid with the walls of the container is

1. Acute angle
2. Obtuse angle
3. 900
4. 00

Answer: (d) 00

Q4: Raindrops are spherical in shape because of

1. Capillary
2. Surface Tension
3. Downward motion
4. Acceleration due to gravity

Answer: (b)Surface Tension

Q5: In a surface tension experiment with a capillary tube, the water rises up to 0.1m. If the same experiment is repeated on an artificial satellite which is revolving around the earth. The rise of water in a capillary tube is

1. 0.1 m
2. 9.8 m
3. 0.98 m
4. Full length of the capillary tube

Answer: (d) Full length of the capillary tube

Q6: At the critical temperature, the surface tension of the liquid

1. Is zero
2. Is infinity
3. Is the same as that at the other temperature
4. Cannot be determined

Answer: (a) Is zero

Q7: The surface of the water in contact with the glass wall is

1. Plane
2. Concave
3. Convex
4. Both a and b

Answer: (b) Concave

Q8: When a soap bubble is charged

1. It contracts
2. It expands
3. It does not undergo any change in size
4. None of these

Answer: (b) It expands

Q9: If common salt is dissolved in water, then the surface tension of saltwater is

1. Increased
2. Decreased
3. Not changed
4. First increases then decrease

Answer: (a) Increased

Q10: A drop of oil is placed on the surface of the water. Which of the following statements is correct?

1. It will remain on it as a sphere
2. It will spread as a thin layer
3. It will partly be as spherical droplets and partly as thin films
4. It will float at the distorted drop on the water surface.

Answer: (b) It will spread as a thin layer

ohms law

Q1: If a current of 5 Amperes flows through the conductor. The number of electrons per second will is

1. 1.6 x 10-19
2. 3.12 x 1019
3. 4 x 1019
4. 7.68 x 1020

Answer: (b) 3.12 x 1019

Q2: Ohm’s law is true for

1. Metallic conductors at low temperature
2. Metallic conductors at high temperature
3. For electrolytes, when current passes through them
4. For diode when current flows

Answer: (a) Metallic conductors at low temperature

Q3: An example of non-ohmic resistance is

1. Diode
2. Tungsten wire
3. Carbon resistance
4. Copper wire

Answer: (a) Diode

Q4: In a conductor, if 6-coulomb charge flows for 2 seconds. The value of electric current will be

1. 3 ampere
2. 3 volts
3. 2 amperes
4. 2 volts

Answer: 3 amperes

Q5: An EMF source of 8.0 V is connected to a purely resistive electrical appliance. An electric current of 2.0 A flows through it. What is the resistance offered by the electrical appliances?

1. 4 ohm
2. 6 ohm
3. 2 ohm
4. 3 ohm

Answer: (a) 4 ohm

Q6: A potential difference of 10 V is applied across a conductor whose resistance is 2.5 ohm. What is the value of current flowing through it?

1. 4 amperes
2. 2 amperes
3. 6 amperes
4. 10 amperes

Answer: (a) 4 amperes

Q7: If the conductor resistance is 50 ohm and the current passing through it is 5 A. What is the value of potential difference?

1. 150 V
2. 250 V
3. 50 V
4. 15 V

Answer: (b) 250 V

Q8: When the length of the conductor is doubled and the area of cross-section remains the same then its resistance

1. Remains the same
2. Will be doubled
3. Will become half
4. Will increase by four times

Answer: (b) Will be doubled

Q9: The current passing through a resistor in a circuit is 1 A when the voltage across the same resistor is 10 V. What is the value of current when the voltage across the resistor is 8 V

1. 0.8 A
2. 8 A
3. 80 A
4. 18 A

Answer: (a) 0.8 A

Q10: Two resistors R1 and R2 with resistance 5 ohms and 10 ohms respectively are connected in series. The voltage across R1 is 4 V. What will be the value of current across R2.

1. 0.8 A
2. 8 A
3. 80 A
4. 18 A

Answer: (a) 0.8 A

Ondielectrics

Q1: Which among the following is a dielectric?

1. Copper
2. Aluminium
3. Plastic
4. Ceramic

Answer: (d) Ceramic

Q2: How can a dielectric be converted to a conductor?

1. Compression
2. Heating
3. Expanding
4. Freezing

Answer:(b) Heating

Q3: Which of the following statements is true for a dielectric?

1. Dielectrics are superconductors at high temperature
2. Dielectrics are superconductors at low temperature
3. The cannot become superconductors
4. They have very less breakdown voltage

Answer:(b) Dielectrics are superconductors at low temperature

Q4: Dielectric materials do not have

1. Free electrons
2. Bound charge
3. Proton
4. neutron

Answer: (a) Free electrons

Q5: Dielectric materials are basically

1. Insulators
2. Semiconductors
3. Superconductors
4. conductors

Answer: (a) insulators

Q6: Find the dielectric constant for material with electric susceptibility of 5

1. 4
2. 6
3. 7
4. 3

Answer: (b) 6

Q7: When the air in a capacitor is replaced by a medium of dielectric constant K, the capacity

1. Deceases K times
2. Increases K times
3. The K2 times
4. Remains constant

Answer: (b) Increases K times

Q8: The dielectric constant cannot be

1. Infinity
2. 5
3. 6
4. 7

Answer: (a) Infinity

Q9: A capacitor of capacity C=10μF is connected to a constant voltage battery of 12 V. Now space between plates is filled with a liquid of dielectric constant 5. The charge that flows now from the battery to the capacitor is

1. 120 μC
2. 699 μC
3. 480 μC
4. 24 μC

Answer: (c) 480 μC

Q10: The capacitance of a parallel plate capacitor is C. If a dielectric slab of thickness equal to one-fourth of the plate separation and dielectric constant K is inserted between the plates, then the capacitance becomes

1. KC/2(K+1)
2. 2KC/K+1
3. 5KC/4K+1
4. 4KC/3K+1

Answer: (d) 4KC/3K+1

Mirror formula based

Q1: A convex mirror of focal length f forms an image which is 1/n times the object. The distance of the object from the mirror is

1. (n-1)f
2. (n-1/n) f
3. (n+1/n) f
4. (n+1) f

Answer: (a) (n-1)f

Q2: Consider a concave mirror of focal length 50 cm. Where should the object be placed so that its image is twice the size of the object and inverted

1. 60 cm
2. 70 cm
3. 75 cm
4. 55 cm

Answer: (c) 75 cm

Q3: An object 2 cm high is placed at a distance of 16 cm from a concave mirror, which produces 3 cm high inverted image. What is the focal length of the mirror?

1. -10 cm
2. -9.6 cm
3. 9.6 cm
4. 8 cm

Answer: (b) -9.6 cm

Q4: An erect image 3 times the size of the object is obtained with a concave mirror of radius of curvature 36 cm. What is the position of the object?

1. -12 cm
2. 5 cm
3. 10 cm
4. -21 cm

Answer: (a) -12 cm

Q5: An object is placed at infinity in front of the convex mirror of radius of curvature 40 cm. How far is the image behind the mirror?

1. 20 cm
2. 25 cm
3. 30 cm
4. 35 cm

Answer: (a) 20 cm

Q6: The image formed by a convex mirror of focal length 30cm is a quarter of the object. What is the distance of the object from the mirror?

1. -90 cm
2. 60 cm
3. -75 cm
4. -60 cm

Answer: (a) -90 cm

Q7: Convex mirror is used to form an image of the object. Which of the following statements is wrong?

1. The image is erect
2. The image is diminished in size
3. The image is real
4. The image lies between the pole and the focus

Answer: (c) The image is real

Q8: A lens having a focal distance of 30 cm is placed in front of an object, which is located at 1m from it. Where is an image of the object located?

1. 40 cm
2. 42.85 cm
3. 52 cm
4. 60 cm

Answer: (b) 42.85 cm

Q9: The focal length of a concave mirror is f and the distance from the object to the principle focus is x. The ratio of the size of the image to the size of the object is

1. (f + x)/f
2. f/x
3. f2/x2

Answer: (b) f/x

Q10: In a concave mirror experiment, an object is placed at a distance x1 from the focus and the image is formed at a distance x2 from the focus. The focal length of the mirror would be

1. x1x2
2. (x1+x2)/2
3. √x1x2
4. √x1/x2

Answer: (c) √x1x2

Moving Coil Galvanometer

Q1: The deflection θ is related to the electric current I in a galvanometer by the relation

1. I ∝ θ
2. I ∝ tan θ
3. I ∝ sin θ
4. I ∝ cos θ

Answer: (a) I ∝ θ

Q2: A moving coil galvanometer carries a current I and the magnetic field B is radial. The coil has N number of turns and an effective area A. The torque acting on the coil of a moving coil galvanometer is given by

1. NA2B2I
2. NABI2
3. NABI
4. N2ABI

Answer: (c) NABI

Q3: The sensitivity of a moving coil galvanometer can be increased by decreasing

1. The number of turns in the coil
2. The area of the coil
3. The magnetic field
4. The couple per unit twist of the suspension

Answer: (d) The couple per unit twist of the suspension

Q4: In ballistic galvanometer, the frame on which the coil is wound is non-metallic. It is

1. To avoid the production of induced e.m.f
2. To avoid the production of eddy currents
3. To increase the production of eddy currents
4. To increase the production of induced e.m.f

Answer: (b) To avoid the production of eddy currents

Q5: The reason the coil is bound over the metallic frame in moving coil galvanometer is

1. The metallic frame helps in oscillation
2. The metallic frame helps in making steady deflection without any oscillation
3. The metallic frame increases the magnetic field
4. None of the above

Answer: (b) The metallic frame helps in making steady deflection without any oscillation

Q6: The deflection in moving coil galvanometer is

1. Inversely proportional to the area of the coil
2. Directly proportional to the torsional constant
3. inversely proportional to the current flowing
4. Directly proportional to the number of turns of the coil

Answer: (d) Directly proportional to the number of turns of the coil

Q7: The pole pieces of the magnet used in a pivoted coil galvanometer are

1. Plane surfaces of a horse-shoe magnet
2. Cylindrical surfaces of a bar magnet
3. Plane surfaces of a bar magnet
4. Cylindrical surfaces of a horse-shoe magnet

Answer: (d) Cylindrical surfaces of a horse-shoe magnet

Q8: A current-carrying rectangular coil placed in a uniform magnetic field. In which orientation will the coil rotate?

1. In any orientation
2. The magnetic field is parallel to the plane of the coil
3. The magnetic field is at 450 with the plane of the coil
4. The magnetic field is perpendicular to the plane

Answer: (d) The magnetic field is perpendicular to the plane

Q9: What is the shape of a magnet in moving coil galvanometer to make the radial magnetic field?

1. Convex cylindrical magnet
2. Horse-shoe magnet
3. Concave cylindrical magnet
4. None

Answer: (c) Concave cylindrical magnet

Q10: Phospher- bronze wire is used in suspension because it has

1. A large couple per unit twist
2. A small couple per unit twist
3. Low conductivity
4. High Sensitivity

Answer: (b) A small couple per unit twist

electric flux

Q1: If a unit positive charge is kept in the air. Then the total flux coming out of unit charge is

1. 4πε0-1
2. 4πε0
3. ε0-1
4. ε0

Answer: (c)ε0-1

Q2: What is the value of electric flux (Φ) on a plane of area 1m2 on which an electric field of 2 V/m crosses with an angle of 300.

1. 1 Vm
2. 2 Vm
3. 3 Vm
4. 4 Vm

Answer: (a) 1 Vm

Q3: Determine the electric flux of a flat square having an area of 10m2 is a uniform electric field of 8000 N/C passing perpendicular to it

1. 8 x 105 Nm2/C
2. 8 x 104 Nm2/C
3. 16 x 105 Nm2/C
4. 4 x 104 Nm2/C

Answer: (b) 8 x 104 Nm2/C

Q4: A plane surface is rotated in a uniform electric field. When is the flux of the electric field through the surface maximum?

1. When the surface is perpendicular to the field
2. When the surface is parallel to the field
3. When the surface is at an angle of 300 with the field
4. When the surface is at an angle of 450 with the field

Answer: (a) When the surface is perpendicular to the field

Q5: When is the flux through a surface taken as positive

1. When the flux lines are directed inwards
2. When the flux lines are directed outwards
3. No flux lines through the surface
4. Flux lines are parallel to each other

Answer: (b) When the flux lines are directed outwards

Q6: The net charge through a closed surface in a given medium depends on

1. Size of the surface
2. Charge of the surface
3. The shape of the surface
4. Area of the surface

Answer: (b) Charge of the surface

Q7: The dimension of electric flux is

1. [M2L2T3A1]
2. [MLT-3A-1]
3. [M3L3T-3A-1]
4. [ML3T -3A-1]

Answer: (d) [ML3T -3A-1]

Q8: The electric flux through a cubical Gaussian surface enclosing net charge q is q/ε0. While the electric flux through one face of a cube is

1. q/ε0
2. q/6ε0
3. q/4πε0
4. q/4ε0

Answer: (b) q/6ε0

Q9: A point charge q is placed at a distance a/2 directly above the centre of the square of side a. The electric flux through the square is

1. q/ε0
2. q/6ε0
3. q/4πε0
4. q/4ε0

Answer: (b) q/6ε0

Explanation for Q9: Imagine a cube with charge q at the centre and the given square is one of its faces. So electric flux through the given square( one face) q/6ε0