General Physics MCQ with Answers

1) The wavelength of the first spectral line in the Balmer series of hydrogen atom is 6561 A^o,The wavelength of the second spectral line in the Balmer series of singly-ionized helium atom is

Answer is:

1215A^o

Explanation:

(1/(λ₁)= (1)²((1/(2²))-(1/(3²)))
=>(1/(λ₂)= (2)²((1/(2²))-(1/(4²)))
=>(λ₂)/(λ₁)=(5*4*16)/(4*4*9*12)= 5/27
=>(λ₂) = (6561*5)/27 = 1215A ^o

2) A police car with a siren of frequency 8kHz is moving with uniform velocity 36km/hr towards a tall building which reflects the sound waves. The speed of sound in air is 320 m/s. The frequency of the siren heard by the car driver is

Answer is:

8.50 kHz

Explanation:

frequency reflected by wall f’
f’ = 8 *10³[ 320/(320 - 10)]
frequency heared by car driver f″= [(320 + 10)/320]f’
f″ = 8* 10³ (32/31) *(33/32) =8.50 kHz

3) An electron and a proton are moving on straight parallel paths with same velocity. They enter a semi-infinite region of uniform magnetic field perpendicular to the velocity. Which of the following statement(s) is/are true ?

Answer is:

They will come out travelling along parallel paths

Explanation:

r = mv/qB
They go in different direction but come out along parallel paths.
T = 2(π) m/qB
as m is different, so T is also different

4) A spherical metal shell A of radius R_A and a solid metal sphere B of radius R_B(< R_A) are kept far apart and each is given charge ’+Q’. Now they are connected by a thin metal wire.Then

Answer is:

((σ_A)/(σ_B)) = ((R_A)/(R_B))

Explanation:

1) E_A = 0

2)(Q_A/R_A) = (Q_B/RQ_B)
=>R_A > R_B
=>Q_A > Q_B

3)σ R = V

4) E = σ/(2 E_o

5) A dense collection of equal number of electrons and positive ions is called neutral plasma. Certain solids containing fixed positive ions surrounded by free electrons can be treated as neutral plasma. Let ’?N’ be the number density of free electrons, each of mass ’?m’. When the electrons are subjected to an to electric field, they are displaced relatively away from the heavy positive ions. If the electric field becomes zero, the electrons begin to oscillate about the positive ions wi

Answer is:

((Ne²)/(mE_o))^1/2

Explanation:

ω = θ/T = T^-1
=>D.f. of ((Ne²)/(mE_o))^{1/2 = (((1/L³)*(I²T²)*(ML³T^-2))/(M*(I²T²)))

=> D.f = T^-1}

1) The wavelength of the first spectral line in the Balmer series of hydrogen atom is 6561 Ao,The wavelength of the second spectral line in the Balmer series of singly-ionized helium atom is

1215Ao

2) A police car with a siren of frequency 8kHz is moving with uniform velocity 36km/hr towards a tall building which reflects the sound waves. The speed of sound in air is 320 m/s. The frequency of the siren heard by the car driver is

8.50 kHz

3) An electron and a proton are moving on straight parallel paths with same velocity. They enter a semi-infinite region of uniform magnetic field perpendicular to the velocity. Which of the following statement(s) is/are true ?

They will come out travelling along parallel paths

4) A spherical metal shell A of radius RA and a solid metal sphere B of radius RB(< RA) are kept far apart and each is given charge ’+Q’. Now they are connected by a thin metal wire.Then

((σA)/(σB)) = ((RA)/(RB))

((Ne2)/(mEo))1/2

1) The wavelength of the first spectral line in the Balmer series of hydrogen atom is 6561 A^o,The wavelength of the second spectral line in the Balmer series of singly-ionized helium atom is

1215A^o

4) A spherical metal shell A of radius R_A and a solid metal sphere B of radius R_B(< R_A) are kept far apart and each is given charge ’+Q’. Now they are connected by a thin metal wire.Then

((σ_A)/(σ_B)) = ((R_A)/(R_B))

((Ne²)/(mE_o))^1/2