16. If ε₀ and µ₀ are the electric permittivity and magnetic permeability in vacuum, ε and µ are corresponding quantities in medium, then refractive index of the medium is

1. 1. 	ε
      	ε0

   
   
   

   2. 	ε0μ
      	εμ0

   
   
   

   3. 	ε0μ0
      	εμ

   
   
   

   4. 	ε0
      	ε0μ0

   
   
   

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1. View Hint View Answer Discuss in Forum

   We know that velocity of electromagnetic wave in vacuum
   

   v0 =	1
   	√μ0∊0

   
   and velocity of electromagnetic wave in medium is
   

   v =	1
   	√μ∊

   
   Therefore refractive index of the medium
   

   (μ) =	Vel of E.M. wave in medium (v0)
   	Vel of E.M. wave in medium (v)

   
   

   =	1/√μ0∊0
   	1/√μ∊

   
   

   	με
   	μ0ε0

   Correct Option: D

   We know that velocity of electromagnetic wave in vacuum
   

   v0 =	1
   	√μ0∊0

   
   and velocity of electromagnetic wave in medium is
   

   v =	1
   	√μ∊

   
   Therefore refractive index of the medium
   

   (μ) =	Vel of E.M. wave in medium (v0)
   	Vel of E.M. wave in medium (v)

   
   

   =	1/√μ0∊0
   	1/√μ∊

   
   

   	με
   	μ0ε0

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17. Which of the following, is the longest wave ?

1. 1. X-rays ​

   
   
   

   2. ​γ-rays

   
   
   

   3. microwaves ​

   
   
   

   4. radio waves

   
   
   

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1. View Hint View Answer Discuss in Forum

   Rays	Wavelength [Range in m]
   X-rays	1 × 10–11 to 3 × 10–8
   γ-rays	6 × 10–14 to 1 × 10–11
   Microwaves	10–3 to 0.3
   Radiowaves	10 to 104

   Correct Option: D

   Rays	Wavelength [Range in m]
   X-rays	1 × 10–11 to 3 × 10–8
   γ-rays	6 × 10–14 to 1 × 10–11
   Microwaves	10–3 to 0.3
   Radiowaves	10 to 104

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18. The frequency of electromagnetic wave, which is best suited to observe a particle of radius 3 × 10^–4 cm is of the order of​​

1. 1. 10¹⁵

   
   
   

   2. ​10¹⁴

   
   
   

   3. 10¹³

   
   
   

   4. 10¹²

   
   
   

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1. View Hint View Answer Discuss in Forum

   ​Size of particle
   

   = λ =	c
   	v

   
   

   3 × 10-6 =	3 × 108
   	v

   
   ν = 10¹⁴ Hz
   ​However, when frequency is higher than this, wavelength is still smaller. Resolution becomes better.

   Correct Option: B

   ​Size of particle
   

   = λ =	c
   	v

   
   

   3 × 10-6 =	3 × 108
   	v

   
   ν = 10¹⁴ Hz
   ​However, when frequency is higher than this, wavelength is still smaller. Resolution becomes better.

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19. The energy of the em waves is of the oder of 15 keV. To which part of the spectrum does it belong?

1. 1. ​Infra-red rays ​

   
   
   

   2. Ultraviolet rays

   
   
   

   3. ​γ-rays ​

   
   
   

   4. X-rays

   
   
   

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1. View Hint View Answer Discuss in Forum

   Energy of x-ray is (100 ev to 100 kev) ​Hence energy of the order of 15 kev belongs to x-rays.

   Correct Option: D

   Energy of x-ray is (100 ev to 100 kev) ​Hence energy of the order of 15 kev belongs to x-rays.

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20. The condition under which a microwave oven heats up a food item containing water molecules most efficiently is​​

1. 1. ​the frequency of the microwaves has no relation with natural frequency of water molecules.

   
   
   

   2. ​microwaves are heat waves, so always produce heating.

   
   
   

   3. ​infra-red waves produce heating in a microwave oven.

   
   
   

   4. the frequency of the microwaves must match the resonant frequency of the water molecules.

   
   
   

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1. View Hint View Answer Discuss in Forum

   Required condition : Frequency of microwaves = Resonant frequency of water molecules.

   Correct Option: D

   Required condition : Frequency of microwaves = Resonant frequency of water molecules.

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