Imagine a carnot engine has a hot reservoir of 680 k and a cold reservoir of 220 k. what is the efficiency of the engine? 58.3% 75.9% 62.3% 72.1% 67.6%

the other person's right, it's E. 67.6% for plato users :)

This question is in complete, the missing table is uploaded along this answer.

the maximum possible kinetic energy K of the electrons emitted from this new surface is 4.9 eV

Explanation:

Given the data in the question;

copper K = 2.7 eV

If the copper is replaced with a piece of sodium ( Na )

the maximum possible kinetic energy K of the electrons emitted from this new surface = ?

we know that;

Kinetic energy of emitted electrons can be written as;

K = hv - hv₀

where v is frequency, h is Plank's constant, and hv₀ is work function of metal

so lets make hv the subject of formula;

hv = K + hv₀

from the table below, work function of copper is 4.5 eV

so we substitute

hv = 2.7 eV + 4.5 eV

hv = 7.2 eV

Now, If the copper is replaced with a piece of sodium ( Na )

we have;

K = hv - hv₀

from the table below, work function of Sodium is 2.3 eV

so we substitute

K = 7.2 eV - 2.3 eV

K = 4.9 eV

Therefore,  the maximum possible kinetic energy K of the electrons emitted from this new surface is 4.9 eV