Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

Consider a light wave that passes from air into a very thick clear glass block that has its opposite internal side mirrored (facing into the glass). The light ray passes into the glass block at an angle greater than $0^{\circ}$ and less than $90^{\circ}$, strikes the mirrored surface and reflects back through the glass into the air.
What happens while the light ray is in the glass block but before it strikes the mirrored surface?

  1. The frequency of the waves increases

  2. The frequency of the waves decreases

  3. The wavelength of the waves decreases

  4. The velocity of the waves decreases

  5. The period of the waves increases
Reveal answer Fill a bubble to check yourself
C,D Correct answer
Explanation

When a light ray enters in a medium of higher refractive index from a lower one, the speed of the wave decreases as $v=\dfrac{c}{\mu}$

Since $\lambda=\dfrac{v}{\nu}$ and the frequency remains unchanged,
$\lambda=\dfrac{\lambda _0}{\mu}$
Hence the wavelength and the velocity of the waves decreases.

Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

Assertion (A) : Velocity of light is more in rarer medium than in denser medium
Reason (R) : Light waves are longitudinal mechanical waves

  1. Statement A is correct R is wrong

  2. Statement A is correct R is right

  3. Statement A and R both are correct but R is not explaining A

  4. Statement A and R both are correct and R is explaining A
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Velocity of light is more in rarer medium than in denser medium because speed of light in a medium is given by $\dfrac{c}{\mu }$ where, c is speed of light in vacuum and $\mu $ is refractive index of medium. Since denser medium has more $\mu $ than rarer medium, the speed of light is less in medium. Light waves are transverse electromagnetic waves.

Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light


(A) Light is a form of electromagnetic radiation and non-mechanical waves.
(B) Light waves do not require a material as a medium for propagation.

  1. Only A is true.

  2. Only B is true.

  3. Both A and B are true.

  4. Both A and B are false.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Both A and B are true,
Light is a form of electromagnetic radiation and a non-mechanical wave. It does not require a material as a medium for propagation. Hence, it can travel through space.

Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

An observer is moving with half the speed of light towards stationary microwave source emitting waves at frequency 10 GHz. What is the frequency of the microwave measured by the observer ?(speed of light = $3 \times10^{8} \ ms^{-1}$)

  1. 15.3 GHz

  2. 10.1 GHz

  3. 12.1 GHz

  4. 17.3 GHz
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Doppler effect in light ( speed of observer is not very small compared to speed of light )
$f^{1} = \sqrt{\dfrac{1+V/C}{1-V/C}} f _{source} = \sqrt{\dfrac{1+1/2}{1-1/2}} (10\ GHz)$
$=17.3\ GHz$


Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

In frounhofer diffraction by a single slit, a position where first order minimum is formed by the wave length $6000\mathring { A } $, first order maximum is formed due to unknown wavelength, the unknown wavelength is

  1. $5000\mathring { A } $
  2. $6000\mathring { A } $
  3. $4000\mathring { A } $
  4. $9000\mathring { A } $
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In single-slit diffraction, the condition for minima is a*sin(theta) = n*lambda. For the first order minimum, a*sin(theta) = 1 * 6000 A. For the first order maximum, the condition is a*sin(theta) = (n + 1/2) * lambda_unknown. Setting these equal, 6000 = 1.5 * lambda_unknown, so lambda_unknown = 4000 A.

Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

Two monochromatic light source, A and B , emit the same number of photons wavelength of A is $ \lambda _A = 400 nm $, and that of $ \lambda _B =600 nm $. the power of radiated

  1. equal to that of source A

  2. less than that source A

  3. greater than that of source A

  4. can not be compared to that source A using the available data
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

The wavelength of a monochromatic light in vacuum is $\lambda$. If travels from vacuum to a medium of absolute refractive index $\mu$. The ratio of wavelength of the incident and refracted wave is

  1. $\mu^2 : 1$

  2. 1 : 1
  3. $\mu$ : 1
  4. 1:$\mu$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

${ \left{ \mu \lambda  \right}  } _{ vacuum }={ \left{ \mu \lambda  \right}  } _{ medium }\ \Rightarrow \dfrac { { \lambda  } _{ i } }{ { \lambda  } _{ r } } =\dfrac { \mu  }{ 1 } \ \therefore \ Ratio\ is\ \mu :1$

Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

The frequency of light of wave length 5000 $\mathring {A}$ is

  1. $1.5 \times 10^5 Hz$
  2. $6 \times 10 Hz$
  3. $6 \times 10^{14} Hz$
  4. $7.5 \times 10^{15} Hz$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Answer is B.

The relation between the velocity of light, frequency and wavelength is given as v = f$\lambda $.
The velocity of light v = $3 \times 10^{8}m/s$.
So, f = $v/\lambda $ = $3 \times 10^{8}m/s / 5000\mathring{A}$ = $6 \times 10^{14} Hz$.
Hence, the frequency of the light is $6 \times 10^{14} Hz$.

Multiple choice physics oscillations and waves huygen's wave theory refraction of water waves reflection and refraction at plane surfaces theories on light

When a ray of light is refracted, the wavelength of the refracted light changes. Identify which of the following explain this phenomenon?
I. Some of the energy of the incident ray is carried away by the reflected ray
II. The boundary surface absorbs some of the energy of the incident ray
III. The incident and refracted rays do not travel with the same velocity

  1. I only

  2. II only

  3. III only

  4. I and II only

  5. I, II, and III
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Wavelength of the light in a medium $\lambda _m = \dfrac{v _m}{\nu}$ where $v _m$ is the velocity of light in that medium
The velocity with which the incident and the refracted ray travels is not same but the frequency of both the rays is same. Hence the wavelength of the refracted light changes w.r.t the incident light.
Hence option C is correct.