Question

The wavelength of red light is 6500A. If velocity of light is 3x 10power 8m/s, then its time
period is ...
A) 1.62x10-15
B) 2.16x10-15
C) 2.76x10-15 D) 1.16*10-15
​

Answer 1

Answer:-

Time period is 2.16 × 10⁻¹⁵ [Option.B]

Explanation:-

We have :-

→ Wavelength of red light = 6500 Å

= 6.5 × 10⁻⁷ m

→ Velocity of light = 3 × 10⁸ m/s

________________________________

Firstly let's calculate the frequency of the red light. We know that :-

ν = c/λ

⇒ ν = [3×10⁸]/[6.5×10⁻⁷]

⇒ ν = 0.46 × 10¹⁵

⇒ ν = 4.6 × 10¹⁴ Hz

Now :-

T = 1/ν

⇒ T = 1/[4.6 × 10¹⁴]

⇒ T = 0.216 × 10⁻¹⁴

⇒ T = 2.16 × 10⁻¹⁵ second

Answer 2

Given :-

Wavelength of red light = 6500 A

Velocity of light = $\bf 3 \times 10^8$

To Find :-

Time period

Solution :-

$\sf \lambda = 6500 = 6500\times 10^{-7}m$

Now,

$\sf \bar{v} = \dfrac{c}{\lambda}$

$\sf \bar{v} = \dfrac{3\times 10^8 }{6500 \times 10^{-7}}$

$\sf\bar{v} = 4.6\times 10^{14}$

Finding time period

T = 1/v

T = 1/4.6 × 10¹⁴

T = 0.216  × 10¹⁴

T = 0.216  × 10⁻¹⁵

K N O W M O R E

SI unit of time is second

SI unit of frequency is Hertz

SI unit of wavelength is meter