The wavelength of the light beam required to turn back all the ejected electrons is 497 nm which is option (b).
- Work function is a material property defined as the minimum amount of energy required to infinitely remove electrons from the surface of a particular solid.
- The potential difference required to support all emitted electrons is called the stopping potential which is given by
.....(1) - where
is the stopping potential and e is the charge of the electron given by
.
It is given that work function (Ф) of monochromatic light is 2.50 eV.
Einstein photoelectric equation is given by:
....(2)
where K.E(max) is the maximum kinetic energy.
Substituting (1) into (2) , we get

As we know that
....(3)
where Speed of light,
and Planck's constant , 
From equation (3) , we get

Learn about more einstein photoelectric equation here:
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A graph of real speed can have a section that's as steep as you want,
but it can never be a perfectly vertical section.
Any vertical line on a graph, even it it's only a tiny tiny section, means
that at that moment in time, the speed had many different values.
It also means that the speed took no time to change from one value to
another, and THAT would mean infinite acceleration.
Generally, the length of the line will indicate how strong the force is. If you have two opposing forces and one is higher than the other, you would draw the line of the higher force visibly longer.
Answer:
60.025m.
Explanation:
S= ut + at^2/2 (2nd equation of motion)
S= 0 + (9.8)(3.5)^2 /2 (free fall case, initial velocity = 0)
S = 4.9 x 12.25
S= 60.025 m.
Disclaimer: did math in my head, so you better double check with a calculator.