Answer:
0.714 m
Explanation:
From the question,
v = λf......................... Equation 1
Where v = velocity of visible light, f = frequency of visible light, λ = wave length of visible light.
make λ the subject of the equation
λ = v/f.................. Equation 2
Given: f = 4.2×10⁸ Hz
Note: Light is an electromagnetic wave, and all electromagnetic waves travels with the same speed (3×10⁸ m/s)
Constant: v = 3×10⁸ m/s
Substitute these values into equation 2
λ = 3×10⁸/4.2×10⁸
λ = 0.714 m
To solve this problem it is necessary to apply the concepts related to Current and Load.
The current in terms of the charge of an electron can be expressed as

Where,
q = Charge
t = time
At the same time the Charge is the amount of electrons multiplied by the amount of these, that is
q = ne
Replacing in the first equation we have to


Clearing n,

Here the time is one second then



Therefore the number of electrons per second are passing any cross sectional area of the wire are 
Gravitational Potential Energy GPE = mg∆h. 12. A 5.0 kg mass is initially sitting on the floor when it is lifted onto a table 1.15 meters high at.
Answer:

Explanation:
Given
-- initial velocity
--- height
Required
Determine the time to hit the ground
This will be solved using the following motion equation.

Where

So, we have:


Subtract 30.2 from both sides





Solve using quadratic formula:

Where




Split the expression
or 
or 
Time can't be negative; So, we have:


Hence, the time to hit the ground is 1.82 seconds