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

Calculate the wavelength of light when it passing through diamond whose refractive index is 2.4 given that wavelength of light in air is 500 nm.

  1. 208 nm

  2. 357 nm

  3. 500 nm

  4. 700 nm

  5. 1,200 nm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given :   $n = 2.4$              $\lambda _a = 500$ nm

$\therefore$ Wavelength of light in diamond        $\lambda _d = \dfrac{\lambda _a}{n}  =\dfrac{500}{2.4} =208$  nm

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

Ray optics holds good when characteristic dimensions are

  1. Of the same order as the wavelength of light

  2. Much smaller than the wavelength of light

  3. Of the order of one millimetre

  4. Much larger than the wavelength of light
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Ray optics holds good when characteristic dimensions are much larger than the wavelength of light.

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

What is the wavelength of light for the least energetic photon emitted in the Lyman series of the hydrogen spectrum. (take hc = 1240 eV nm)

  1. 102 nm

  2. 150 nm

  3. 82 nm

  4. 122 nm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Find out $\lambda$ of light

$hc=1240eVmm$
Lymen series of the hydrogen spectrum
Solution
For any series the transistion that produces the least energetic photon is the transition between the home base level that defines the series and the level immediately above it. For the hymen series, the home-base level is at $n=1$
So the transition that produces the least energetic photon is the transition from the $n=2$ level to then $n=1$ level.
$\therefore$ The wavelength for the least energetic photon is
$\lambda=\cfrac{hc}{E _2-E _1}$
Here $hc=1240eVnm$
$E _1=-\cfrac{13.6}{1^2}eV\ \quad=-13.6eV$
(as $E _n=-\cfrac{13.6}{n^2}eV)$
$E _2=-\cfrac{13.6}{2^2}eV\ \quad=-3.4eV\ \therefore\lambda=\cfrac{1240eVnm}{-3.4eV-(-13.6eV)}\ \quad=\cfrac{1240eVnm}{102eV}\ \quad=122nm$

Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

The molecules of medium vibrate about their mean positions during heat transfer in the process of

  1. Conduction

  2. Radiation

  3. Convection

  4. None
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The molecules of medium transfer heat as they vibrate about mean position in conduction.
The molecules of medium absorb heat, they rise and other molecules of medium come to take their place convection
In radiation, medium does not play role.

Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

Air is a bad conductor of heat because:

  1. it's molecules are in continuous contact with each other.

  2. it's molecules are not in continuous contact with each other

  3. it's molecules absorb all the heat

  4. it's molecules are moving randomly due to Brownian motion
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Air is a bad conductor of heat because it's molecules are not in continuous contact with each other.
Air molecules are too far to disperse heat energy to one another efficiently. Heat is conducted by molecules and atoms that are very closely bonded together and vibrating at high frequency.
Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

.................. surface absorbs more heat than any other surface under identical conditions.

  1. White & Shiny

  2. White & Rough

  3. Black & Rough

  4. Yellow & Shiny
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Black & rough surface absorbs more heat than any other surface under identical conditions.
Black surface absorbs all the radiations more easily than any surface as its absorptivity is $1$.
Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

The heat transfer in air is poor because

  1. it take place mainly due to convection

  2. it take place mainly due to conduction

  3. it take place mainly due to radiation

  4. all of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Air is a gas and its molecules are far apart from each other. So, this is not a good condition for conduction. Also, air being a non-metal doesn't have free electrons for conduction. Hence option B is not applicable.

C is also not applicable because radiation doesn't need any medium. Air being a fluid, convection can take place through it. But convection is not a very fast mode of transfer of heat.

Multiple choice physics transfer of heat applications of heat conduction applications of insulation clothes - our necessity

Seema is planning a trip to Kashmir this summer. Which of the following clothes should she definitely pack?

  1. Denim Jacket

  2. Leather pants

  3. Woolen sweater

  4. Cotton shirt
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

She must pack the woolen sweater, because even in summer; Kashmir's climate will definitely too much cool. As wool is good insulator of heat; it insulates body from the surrounding. And the air which is trapped between woolen fabrics. It prevents the flow of heat from the body; as air is also bad conductor of heat. So as a result the heat present in the body remains trapped in the body; it can't escape to atmosphere.