If light travels at 3 · 108 m/s and its frequency is 6 · 1015 hz, then its wavelength is: a) 10 · 107 m b) 5 · 10-8 m c) 5 · 10-7 m d) 10 · 10-7 m

 5*10^-8 (B)

Explanation:  

-Given that the light is the speed

-We will be following the formula :

V= f (λ)

Where,  

V is the velocity  

F is the frequency  

λ is the wavelength  

3*10^8 = (6*10^15 )* λ

(3*10^8)/ (6*10^15 ) =  λ

5*10^-8m = λ answer

Note: λ is initially 0.5*10^-7 but to make it in the standard form it should be 5*10^-8. And do not forget to place the unit for the wavelength i.e. meter(m) otherwise you may lose marks!

when a device is used in a circuit in which the voltage is 81 v, the current flowing through the device is 3 a. what is the resistance of the device?

a. 27 ω

b. 40.5 a

c. 243 ω

d. 243 a

the correct answer is a. 27

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.