Physics previous year question Of Modern Physics For NDA
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previous year question Of Modern Physics For NDA

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previous year question
Q 2868080805

Consider the following statements

Solution:

Correct Answer is `=>` (C) 1, 3 and 4
Q 2868880705

If K_alpha radiation of M_0 (Z= 42) has a wavelength of 0.71 A Calculate the wavelength of the corresponding radiation of Cu(Z=29)


(A)

1.52 A

(B)

2.0A

(C)

3.52

(D)

2.52A

Solution:

`:..lambda alpha (1)/()Z-1)^2 => (lambda_1)/(lambda_2) = ((Z_2-1)^2)/((Z_1-1)^2)`
`(0.71)/(lambda_2) = ((29_1)^2)/((42_1)^2) = (28)^2/(41)^2`
`= lambda_2 = 1.52A`
Correct Answer is `=>` (A) 1.52 A
Q 2828880701

The largest distance between the inter-atomic planes of a crystal is 10 A what is the upper limit for wavelength of of X- rays ,which can be usefully studied with this crystal?

(A)

20 A

(B)

40A

(C)

30A

(D)

10A

Solution:

By Bragg's law, `2sintheta = nlambda`
`=> lambda = (2dsintheta)/(n)`
`lambda_max = 2d = 2xx m10 A = 20 A`
Correct Answer is `=>` (A) 20 A
Q 2848780603

A potential difference of 42000 V is used in an X-ray tube to accelerate electrons. The maximum frequency of X-rays produced is `(e = 1.6 xx 10^(-19)` C and `h = 6.63 xx 10 ^9-34) J-s)`

(A)

`10^20`

(B)

`10^16`

(C)

`10^18`

(D)

`10^19`

Solution:

Given, V = 42000V
`e_V = bV_max`
`V_max = (eV)/(b) = (1.6 xx 10(-19) xx 42000)/(6.63xx10^(-34) = 10^19`
Correct Answer is `=>` (D) `10^19`
Q 2888580407

If the distance of 100 W bulb is increased from a photocell, then the saturation current in the photocell varies with distance d as.

(A)

`i alpha (1)/d_2)`

(B)

`i alpha d^2`

(C)

`i alphad`

(D)

`i alpha 1/d`

Solution:

Correct Answer is `=>` (A) `i alpha (1)/d_2)`
Q 2868580405

The frequency of first line of Balmer series in hydrogen atoms is `u_0` jumps, then the frequency u of the line emitted by doubly ionised lithium atom (Li^(2+)) is

(A)

`v_0 //9`

(B)

`9v_0`

(C)

`4v_0`

(D)

`2v_0`

Solution:

Correct Answer is `=>` (C) `4v_0`
Q 2848580403

First speetral line of sodium atom is 5890 A, the first excitation potential is

(A)

10.2 eV

(B)

4.1 eV

(C)

3.7 eV

(D)

2.1 eV

Solution:

Correct Answer is `=>` (D) 2.1 eV
Q 2828580401

Ratio of energy of orbital electron in 4th orbit and 5th orbit of hydrogen atom is.

(A)

4 : 5

(B)

5 : 4

(C)

25: 16

(D)

16: 25

Solution:

Correct Answer is `=>` (D) 16: 25
Q 2848480303

The recoil speed of a hydrogen atom after it emits a photon in going from n = 5 state to n = 1 state is (Rydberg's constant `R 1.097 xx 1^7/m)`

(A)

`4.18m//s`

(B)

`5.18m//s`

(C)

`6.18 m//s`

(D)

`3.18rn//s`

Solution:

Correct Answer is `=>` (A) `4.18m//s`
Q 2818480300

The speed of electron in the ground state of hydrogen atom is.

(A)

`2 xx 10^6 m//s`

(B)

`2 xx 10^5 m//s`

(C)

speed of sound

(D)

zero

Solution:

Correct Answer is `=>` (A) `2 xx 10^6 m//s`
Q 2858380204

The difference in angular momentum associated with the electron in the two successive orbits of hydrogen atom is.

(A)

`h/(2pi)`

(B)

`(2nh)/(pi)`

(C)

`h/2`

(D)

`(n-1) (h)/(2pi)

Solution:

Correct Answer is `=>` (A) `h/(2pi)`
Q 2828380201

The radius of first Bohr's orbit of electron in hydrogen atom is.
`(e = 1.6 xx 10^(-19)C, m + 9.1 x 10(-31) kg, h = 6.6 xx 10-(34) J- S)`

(A)

0.53 mm

(B)

53 A

(C)

0.53 A

(D)

5.3 A

Solution:

Correct Answer is `=>` (C) 0.53 A
Q 2868280105

For light of wavelength 5000 A, the photon energy is nearly 2.5 eV. For X-ray of wavelength 1 A. the photon energy will be close to.

(A)

`((2.5)/(5000))eV`

(B)

`[(2.5)/(5000)^2eV`

(C)

`2.5 xx (5000)^2 eV`

(D)

`[2.5xx 5000) eV`

Solution:

Given, `lamba_1 = 5000 A,lamba_2 A`
`:. E_2 alpha 1/lamba => (E_2)/(E_1) = (lamba_1)/(lamba_2) = (5000)/(1)`
`E_2 = (5000)E_1= (2.5xx5000)eV`
Correct Answer is `=>` (D) `[2.5xx 5000) eV`
Q 2818280100

The energy of photon corresponding to the visible light of maximum wavelength is nearly.

(A)

7 eV

(B)

3.2 eV

(C)

1.6 eV

(D)

1 eV

Solution:

Correct Answer is `=>` (C) 1.6 eV
Q 2888180007

The energy of incident photon is 12.:375 eV while the energy of scattered photon is 9.375 eV. Then, KE of recoil photon is.

(A)

21.75 eV

(B)

more than 3 eV

(C)

less than 3 eV

(D)

3 eV

Solution:

The KE for recoil photon = KE incident + KE scattered = 12.375cV- 9.375eV = 3eV
Correct Answer is `=>` (D) 3 eV
Q 2828180001

The threshold frequency of potassium is `3xx10^14 Hz.` The work function is.

(A)

`0.5:xx10_19 J`

(B)

`4xx10^(-19)J`

(C)

`2xx10(-19) J`

(D)

`10 xx 10^(-19) J`

Solution:

`:. W = bv_0 = 6.626 xx 10^(-34) xx 3 xx 10 ^14`
`[:. v_0 =3 xx 10^14]`
`=19.878 xx 10^(-28) J = m1.98xx 10 (-19)J`
`= 2xx 10^(-19) J`
Correct Answer is `=>` (C) `2xx10(-19) J`
Q 2838178902

Light of wavelength `4000 A` is incident on a metal plate whose work function is e V. What is the maximum KE of emitted photoelectron?

(A)

0.5 eV

(B)

1.1 eV

(C)

1.5 eV

(D)

2.0 eV

Solution:

Given, wavelength, `lambda = 4000A,`
work function, `W_0 = 2eV`
`:. K = ((bc)/(lambda)-W_0)`
`= (6.6xx10^(-34) xx 3 xx 10^8)/(4000xx10^(-10) - 2xx 1.6 xx 10^(-19)`
`= (4.95xx10^(-19) V- 2eV)`
`= (3.09eV- 2eV) = 1.1 eV`
Correct Answer is `=>` (B) 1.1 eV
Q 2818178900

The value of retaining potential needed to stop the photo electrons ejected from a metal surface of work function 1.2 eV with light of energy 2 e V is.

(A)

3.8 V

(B)

1.8 V

(C)

2.8 V

(D)

0.8 V

Solution:

:. Retarding potential
`eV_0 =bv- bv_0 = 2- 1.2 = 0.8 eV`
`=> V_0 = 0.8 V`
Correct Answer is `=>` (D) 0.8 V
Q 2818078809

The specifie charge on an electron is.

(A)

`1.759 xx 10^11C /kg`

(B)

`1 672 xx(-27) c 1 kg`

(C)

`1.62 xx 10^10 C/kg`

(D)

`9.11xx10^21 C/kg`

Solution:

Correct Answer is `=>` (A) `1.759 xx 10^11C /kg`
Q 2868078805

A cathode ray tube is operated at 2500 V. The speed of electron will be.

(A)

`3xx10^7m//s`

(B)

`1.5xx10^7m//s`

(C)

`3.6 xx 10^6m//s`

(D)

`6 xx 10 7m//s`

Solution:

Correct Answer is `=>` (A) `3xx10^7m//s`
Q 2828078801

A cathode ray tube is operated at 2500 V. The speed of electron will be.

(A)

`3xx10^7m//s`

(B)

`1.5xx10^7m//s`

(C)

`3.6 xx 10^6m//s`

(D)

`6 xx 10 7m//s`

Solution:

Correct Answer is `=>` (A) `3xx10^7m//s`
Q 2808878708

Cathode rays have velocity.

(A)

either less or greater than velocity of light c

(B)

less than velocity of light c

(C)

equal to velocity of light c

(D)

greater than velocity of light c

Solution:

Correct Answer is `=>` (B) less than velocity of light c
Q 2888878707

The speed of electron in the orbit of hydrogen atom in ground state is.


(A)

c

(B)

c/2

(C)

c/10

(D)

c/137

Solution:

Correct Answer is `=>` (D) c/137
Q 2818878700

The wave nature of matter was first discovered by.

(A)

C.V. Raman

(B)

Davison and Germer

(C)

de-Broglie

(D)

J. J. Thomson

Solution:

Correct Answer is `=>` (C) de-Broglie
Q 2888778607

Molecular weight of heavy water used as a moderator in nuclear reactor is.

(A)

10

(B)

18

(C)

22

(D)

16

Solution:

Correct Answer is `=>` (B) 18
Q 2878778606

According to Bohr's atomic model, the electron t'evolve around the nucleus in.

(A)

stationary elliptical orbit

(B)

radiating circular orbit

(C)

stationary circular orbit

(D)

arbitrary circular orbit

Solution:

Correct Answer is `=>` (C) stationary circular orbit
Q 2868778605

Electrons in the atom are held due to.

(A)

van der Walls' forces

(B)

gravitational forces

(C)

nuclear forces

(D)

coulomb forces

Solution:

Correct Answer is `=>` (D) coulomb forces
Q 2858778604

Of the following properties, the photon does not possess

(A)

frequency

(B)

momentum

(C)

energy

(D)

rest mass

Solution:

Correct Answer is `=>` (D) rest mass
Q 2848778603

Conversion of light energy into electrical energy is achieved in a

(A)

cloud chamber

(B)

thermocouple

(C)

photocell

(D)

Coolidge tube

Solution:

Correct Answer is `=>` (C) photocell
Q 2828778601

The rest mass of a photon of wavelength `lambda` is

(A)

`hc/lambda`

(B)

`h/lambda`

(C)

`h/clambda`

(D)

zero

Solution:

Correct Answer is `=>` (D) zero
Q 2888678507

The momentum of a photon of wavelength `lambda` is given by

(A)

`1/hlambda`

(B)

`lambda/h`

(C)

`h/lambda`

(D)

`hlambda`

Solution:

Correct Answer is `=>` (D) `hlambda`
Q 2868678505

The photoelectric effect is based on the law of conservation of.

(A)

angular momentum

(B)

linear momentum

(C)

linear mass

(D)

energy

Solution:

Correct Answer is `=>` (D) energy
Q 2848678503

Einstein was awarded noble prize for his.

(A)

explanation of photoelectric effect

(B)

unified field of theory

(C)

general theory of relativity

(D)

special theory of relativity

Solution:

Correct Answer is `=>` (A) explanation of photoelectric effect
Q 2818478309

The work function for photoelectric effect.

(A)

is different for different metals

(B)

is same for all metals

(C)

depends upon the frequency of light

(D)

None of the above

Solution:

Correct Answer is `=>` (A) is different for different metals
Q 2808478308

Photoelectrons are emitted when

(A)

a zinc plate is irradiated with light

(B)

a zinc plate is subjected to high pressure

(C)

a zinc plate is hammered

(D)

a zinc plate is heated

Solution:

Correct Answer is `=>` (A) a zinc plate is irradiated with light
Q 2878478306

The phenomenon of photoelectric effect was explained by.

(A)

Bohr

(B)

Einstein

(C)

Maxwell

(D)

Planck

Solution:

Correct Answer is `=>` (B) Einstein
Q 2858478304

Positive rays were discovered by.

(A)

Bragg's

(B)

Aston

(C)

Goldstein

(D)

Thomson

Solution:

Correct Answer is `=>` (C) Goldstein
Q 2868378205

Which one of the following will be deflected by electric field?

(A)

Ultraviolet rays

(B)

X-rays

(C)

`gamma`-rays

(D)

Cathode rays

Solution:

Correct Answer is `=>` (D) Cathode rays
Q 2848378203

Cathode rays are

(A)

electromagnetic wave

(B)

positively charged

(C)

negatively charged

(D)

neutral

Solution:

Correct Answer is `=>` (C) negatively charged
Q 2828378201

Cathode rays are deflected by.

(A)

Neither electric field nor magnetic field

(B)

Both electric field and magnetic field

(C)

Only electric field

(D)

Only magnetic field

Solution:

Correct Answer is `=>` (B) Both electric field and magnetic field
Q 2878278106

Cathode rays were discovered by.

(A)

Millikan

(B)

Rutherford

(C)

W crookes

(D)

J.J. Thomson

Solution:

Correct Answer is `=>` (D) J.J. Thomson
Q 2858278104

The neutron, proton, electron and alpha particles are moving with equal kinetic energies. How can the particles be arranged in the increasing order of their velocities'?

(A)

Alpha particle-neutron-protonelectron

(B)

Proton-electron-neutron-alpha particle

(C)

Electron-proton-neutron-alpha particle

(D)

Neutron-proton-electron-alpha particle

Solution:

Correct Answer is `=>` (A) Alpha particle-neutron-protonelectron
Q 2774601556

If the potential difference applied to an X-ray tube is doubled while keeping the sepearation between the filament and the target as same, what will happen to the cutoff wavelength ?
NDA Paper 2 2017
(A)

will remain same

(B)

Will be doubled

(C)

will be halved

(D)

Will be four times of the original wavelength

Solution:

Correct Answer is `=>` (C) will be halved
Q 2376591476

Which one of the following is not the characteristic of X-ray?
NDA Paper 2 2007
(A)

No medium is required for their propagation

(B)

They obey laws of reflection

(C)

They travel with the speed of light waves

(D)

They are longitudinal in nature

Solution:

X-rays are electromagnetic in nature, so they are transverse waves.
Correct Answer is `=>` (D) They are longitudinal in nature
Q 2386491377

The question consists of two statements, one labelled as the 'Assertion
(A)' and the other as 'Reason (R) '. You are to examine these
two statements carefully and select the answers to these
items using the codes given below.
NDA Paper 2 2007

Assertion : Radio does not work in a moving train unless aerial is put outside the window.

Reason : The train compartment acts as a hollow cylinder and charge is centred which does not allow radio to work.

(A) Both A and R individually true and R is the correct explanation of A
(B) Both A and R are individually true but R is not the correct explanation of A
(C) A is true but R is false
(D) A is false but R is true
Solution:

The compartment of a moving train acts as a hollow cylinder and charge is centred, due to which radio does not work in a moving train unless aerial is put outside the window.
Correct Answer is `=>` (A)
Q 2316291179

Electromagnetic radiations are emitted by which of the following?
NDA Paper 2 2007
(A)

Only by radio and television transmitting antennas

(B)

Only by bodies at temperature. higher than their surroundings

(C)

Only by red-hot bodies

(D)

By all bodies

Solution:

Electromagnetic radiations are emitted by the bodies at higher temperature than their surroundings.
Correct Answer is `=>` (B) Only by bodies at temperature. higher than their surroundings
Q 2316580479

Which one of the following is correct? The wavelength of the X-rays
NDA Paper 2 2007
(A)

is longer than the wavelength of sound waves

(B)

is longer than the wavelength of the yellow sodium light

(C)

is longer than the wavelength of radio waves

(D)

is of the order of `0.1` nanometer

Solution:

The wavelength of the X-rays is of the order of `0.1` nanometer, i.e., `0.1 xx 10^(-9) m (1 A)`.
Correct Answer is `=>` (D) is of the order of `0.1` nanometer
Q 2316367279

Which one of the following is the range of frequency used in optical communication?
NDA Paper 2 2008
(A)

`10^3-10^4` Hz

(B)

`10^8-10^9` Hz

(C)

`10^13-10^14` Hz

(D)

`10^16-10^17` Hz

Solution:

For optical communication, the range of frequency used is `10^13- 10^14` Hz.
Correct Answer is `=>` (B) `10^8-10^9` Hz
Q 2316167070

Match the following






Column IColumn II
(A) Explanation of the
photoelectric effect 		(1) J J Thomson
(B) Discovery of a comet (2) Robert Millikan
(C) Measurement of the
electronic charge 		(3) Einstein
(D) Thermoelectricity (4) Edmund Halley
(5)Seebeck

NDA Paper 2 2008
(A)

`A-> 3, quad B-> 4, quad C->1, quad D->2`

(B)

`A-> 4, quad B-> 3, quad C->2, quad D->1`

(C)

`A-> 2, quad B-> 3, quad C->4, quad D->5`

(D)

`A-> 3, quad B-> 4, quad C->2, quad D->5`

Solution:

A. Explanation of the photoelectric effect-· Einstein (3)
B. Discovery of a comet- Edmund Halley (4)
C. Measurement of electronic charge- Robert Millikan (2)
D. Thermoelectricity-- Seebeck (5)
Correct Answer is `=>` (D) `A-> 3, quad B-> 4, quad C->2, quad D->5`
Q 2356356274

Match the following







Column IColumn II
(Type of Electromagnetic
Radiation) 		(Approximate
Wavelength in Metre)
(A) Infrared radiation(1) `10^(-12)`
(B) X-rays (2) `10^(-5)`
(C) Ultraviolet radiation (3) `10^(-10)`
(D) Gamma rays (4) `10^(-8)`

NDA Paper 2 2009
(A)

`A-> 3, quad B-> 4, quad C->1, quad D->2`

(B)

`A-> 4, quad B-> 3, quad C->2, quad D->1`

(C)

`A-> 2, quad B-> 3, quad C->4, quad D->1`

(D)

`A-> 4, quad B-> 1, quad C->2, quad D->3`

Solution:

`lambda_(gamma-rays) < lambda_(x-rays) < lambda_(UV-rays) < lambda_(i nf r ared-rays)`

`10^(-12) < 10^(-10) < 10^(-8) < 10^(-5)`

Therefore, correct option is (3).
Correct Answer is `=>` (C) `A-> 2, quad B-> 3, quad C->4, quad D->1`
Q 2316123970

Which one of the following is not electromagnetic in nature?
NDA Paper 2 2009
(A)

Cathode-rays

(B)

X-rays

(C)

Gamma-rays

(D)

Infrared-rays

Solution:

X-rays, gamma rays and infrared rays are part of electromagnetic spectrum whereas cathode rays are not electromagnetic in nature.
Correct Answer is `=>` (A) Cathode-rays
Q 2306023878

Propagation of light quanta may be described by
NDA Paper 2 2009
(A)

Photons

(B)

Protons

(C)

Neutrons

(D)

Electron

Solution:

According to Einstein's quantum theory. light
propagates in the bundles (pacl,ets or quanta) of energy, each
bundle being called a photon and possessing energy
Correct Answer is `=>` (A) Photons
Q 2336023872

Consider the following parts of spectra

1. visible
2. Infrared
3.Ultraviolet
4. microwave


Which one of the following is the correct sequence in which their wavelengths increase?
NDA Paper 2 2009
(A)

4 < 3 < 1 < 2

(B)

4 < 1 < 2 < 3

(C)

3 < 2 < 1 < 4

(D)

3 < 1 < 2 < 4

Solution:

Hence, the increasing order of wavelength is Ultraviolet< Visible< Infrared < Microwave 3<1<2<4
Correct Answer is `=>` (D) 3 < 1 < 2 < 4
Q 2326123071

In vacuum, the speed of light
NDA Paper 2 2009
(A)

depends on its wavelength

(B)

depend on its frequency

(C)

depend on its intensity

(D)

neither depend on its wavelength, frequency nor intensity

Solution:

In vacuum, the speed of light is constant, i.e ..
`3 xx 10^8 m//s`. Hence, it neither depend on its wavelength,
frequency nor intensity.
Correct Answer is `=>` (D) neither depend on its wavelength, frequency nor intensity
Q 2386112977

The wavelength of X-rays is of the order of
NDA Paper 2 2009
(A)

`1 mm`

(B)

`1 cm`

(C)

`1` micron

(D)

`1 overset@A`

Solution:

The wavelength of X-rays is of the order of `1overset@A`.
Correct Answer is `=>` (D) `1 overset@A`
Q 2305678568

When X-rays are produced
NDA Paper 2 2010
(A)

heat is generated at the target

(B)

heat is absorbed at the target

(C)

the temperature of the target remains constant

(D)

brilliant light is seen al the target

Solution:

When X-rays are produced, a stream of highly energetic electrons are focussed at the target (made of tungsten or molybedum). When these energetic electrons fall on the target, most of the energy of these electrons is converted into heat energy and heat is generated at the target.
Correct Answer is `=>` (A) heat is generated at the target
Q 2305578468

Which one of the following pairs of rays is electromagnetic in nature?
NDA Paper 2 2010
(A)

Beta rays and gamma rays

(B)

Cathode rays and X-rays

(C)

Alpha rays and beta rays

(D)

X-rays and gamma rays

Solution:

Beta rays (`beta`-rays) These are either electron (`e^-`) or positrons (`e^ +`)having same mass and one unit electronic charge of negative and positive sign respectively.

Gamma rays (`gamma`-rays) They are highly penetrating electromagnetic waves, carrying no charge or mass.

Cathode rays (`alpha`-rays) Cathode rays are the streams of electrons given off by the cathode of a gas-discharge tube at low temperature.

X-rays X-rays are electromagnetic waves with wavelengths ranging from `0.1 A` to `100 A` (or frequency range `10^16 - 10^19 Hz`)

Alpha rays ( `alpha`-rays) These are positively charged particles (`alpha = text()_2H e^ 4`) having charge twice of a proton and mass four times of a proton.
Correct Answer is `=>` (D) X-rays and gamma rays
Q 2305478368

The ratio of velocity of X-rays to that of `gamma` rays
NDA Paper 2 2010
(A)

is < 1

(B)

is > 1

(C)

is 1

(D)

depends upon tile ratio of their frequencies

Solution:

The X-rays and `gamma` rays are electromagnetic waves. The velocity of electromagnetic wave in vacuum is equal to the velocity of light in vacuum. Hence, electromagnetic wave moves with speed of light in vacuum. Therefore, the ratio of velocity of X- rays to that of `gamma` rays is equal to 1.
Correct Answer is `=>` (C) is 1
Q 2365756665

The visible light has a wavelength range from about `380` nm (violet) to `780` nm (red). If an excited object emits light with wavelength of `15` nm, to which one of the following ranges does it belongs?
NDA Paper 2 2010
(A)

X-ray

(B)

Gamma ray

(C)

Infrared

(D)

Ultraviolet

Solution:

From the above table, it is clear that if an excited object emits light of wavelength 15 nm then it lies in X-ray region
Correct Answer is `=>` (A) X-ray
Q 2315356260

Internet communication uses optical fibre cables because of
NDA Paper 2 2010
(A)

low cost

(B)

free from virus threat

(C)

high data carrying capacity

(D)

faster than light communication of signals

Solution:

Optical fibre has large data carrying capacity (thousands of time greater, reaching speeds up to ·`1.6 TB//s` in field deployed systems and up to `10 TB//s` in lab system).
Correct Answer is `=>` (C) high data carrying capacity
Q 2384391257

Which one among the following waves are called waves of heat energy?
NDA Paper 2 2011
(A)

Radiowaves

(B)

Infrared waves

(C)

Ultraviolet waves

(D)

Miicrowave

Solution:

Radio waves (`10^5 Hz`) are used in telecommunication.
Microwaves are used in radar. Infrared waves are used for
heating and ultraviolet waves are sun rays.
Correct Answer is `=>` (B) Infrared waves
Q 2354167054

Body A of mass 2 kg and another body B of mass 4 kg of same material are kept in the same sunshine for some time interval. If the rise in temperature is equal for both the bodies, then which one among the following in this regard is correct?
NDA Paper 2 2012
(A)

Heat absorbed by B is double because its mass is double

(B)

Heat absorbed by A is double because its mass is equal

(C)

Heat absorbed by both A and B is equal because the quantity of heat absorbed does not depend upon mass

(D)

Heat absorbed by B is four times than the heat absorbed by A because the quantity of heat absorbed is proportional to square of the mass

Solution:

We know that `E = mc^2`

Here, `c ^2` is a constant. So, `E prop m`

Therefore, heat absorbed by `B` is double because its mass is
double
Correct Answer is `=>` (A) Heat absorbed by B is double because its mass is double
Q 2304045858

Yellow colour light is used as fog light because yellow colour
NDA Paper 2 2012
(A)

light is most scattered by fog

(B)

has the longest wavelength among all colours

(C)

has the longest wavelength among all colours except red and oran[Je, but the red colour is already used for brake light and stop light whereas orange colour is avoided due to its similarity with red

(D)

has the shortest wavelength among all colours not already reserved for other purpose

Solution:

Yellow colour light is being used as fog light because it has the longest wavelength among all colours except red and orange but the red colour is already used for brake light and stop light whereas orange colour is avoided due to its similiarity with red.
Correct Answer is `=>` (C) has the longest wavelength among all colours except red and oran[Je, but the red colour is already used for brake light and stop light whereas orange colour is avoided due to its similarity with red
 
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