# NEET Physics Questions and Answer 2020

NEET Physics Questions 2020 which includes all topics. Skkopi provides the twisted questions asked in NEET examination to confuse the students in the exam. These Physics questions help you to crack exam easily!

1.    The decay of radioactive material ‘X’ is 12𝜆 and material ‘Y’ is 4𝜆. Initially they have same number of nuclei. After what time, ratio of number of nuclei material ‘Y’ to that ‘X’ will be 1/e?

a.    1/7𝜆

b.    1/8𝜆

c.    1/9𝜆

d.    1/𝜆

B – 1/8𝜆

If  Ny/Nx = 1/e

Ny/Nx = e-12t/e-4t

1/e = e-8t

-1= -8𝜆t

t = 1/8𝜆

2.      Young’s double slit experiment is first performed in air then in a medium other than air. It is found that 6th bright fringe in the medium lies where 4th dark fringe lies in air. The refractive index of the medium is

a.    1.71

b.    1.25

c.    1.68

d.    1.92

a

A1 =A4th dark = [2 x4 -1]𝜆D/2d

A2 =A6th bright = 6𝜆D/(mu)d

A1 = A2

7𝜆D/2d=6𝜆D/(mu)d

7/2 = 6/mu

mu = 12/7 = 1.71

3.      Two buses moving in opposite direction approach each other ,1st bus speed is 30 m/s. The first bus driver blows horn with frequency 250 Hz. The frequency heard by the 2nd bus driver is 390Hz (Velocity of sound is 340 m/s). What is the speed of 2nd bus?

a.    10.8 m/s

b.    3.5 m/s

c.    35.3 m/s

d.    5.4 m/s

d

f2 =f1[V+V2/V-V1]

390 = 350[340+V2/340-30]

340+V2 = 345.4

V2 = 345.4-340 = 5.4 m/s

4.      An Astronomical refracting telescope with objective lens of large focal length and large diameter will have

a.    Large angular magnification and low angular resolution

b.    Large angular magnification and high angular resolution

c.    Low angular magnification and high angular resolution

d.    Small angular magnification and low angular resolution

5.      For a radioactive material half-life is 20 min. If initially there are 800 nuclei, after one hour how many nuclei remains?

a.    300

b.    400

c.    100

d.    600

c

No of nuclei remaining = 800-x =N

No of nuclei present initially = 800 =No

N/No =(½)n

800-x/800 = (½)t/t/2

= (½)60/20

800 -x /800 = 0.125

800-x = 800 x 0.125

X = 800 -100 = 700

N = 800 – 700 =100

6.      An Object is placed at a distance of 60 cm from a concave mirror of focal length 20 cm. What distance the object to move to get 100 cm displacement of the Image away from the mirror.

a.    32 cm

b.    20 cm

c.    17 cm

d.    40 cm

c

1/f = 1/v + 1/u

-1/20 = 1/v1 – 1/60

1/v1 = -1/20 + 1/60

V1 = -30 cm

Object displaced

-1/20 = 1/100 -1/u2

1/u2 = 1/100 + 1/20

1/u2 = 0.06

U2 = 1/0.06 = 16.67 =17cm

7.      In a common emitter transistor amplifier, the audio signal voltage across the collector is 4v and the resistance of the collector is 5k. If the voltage gain is 200 and the base resistance is 3k, then the power and current of the amplifier is

a.    150 and 1800

b.    230 and 19000

c.    20 and 240

d.    120 and 24000

d

Voltage gain Vg  = 200 V

Current gain  Ig  = Vg x Rb/Rc

Rb = Base resistance

Rc = Collector resistance

= 200 x3/ 5

Ig  = 600/5 = 120 A

Power gain W =Vg x Ig

= 200 x 120

W = 24000 w

8.    The efficiency ratio of heat engine to carnot engine is 6:1. What is the work done if the carnot engine is used as a refrigerator and absorbs 60j energy at lower temperature?

a.    6j

b.    10j

c.    12j

d.    18j

9.      A black body with a diameter 12 cm and radiates 400W power at 400K. If the diameter is doubled and temperature is halved , the power radiated in watts is

a.    200

b.    100

c.    800

d.    1600

10.      A 20 cm long wire with resistance 10 is melted and stretched to 30 cm, then what will be the new resistance

a.    15.8

b.    20.5

c.    22.5

d.    30

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