## Kinetic Energy 1.23 c

$c=\lambda v$

004253593
Posts: 218
Joined: Fri Sep 20, 2013 3:00 am

### Kinetic Energy 1.23 c

1.23 c. What is the wavelength of the radiation that cause photejection of the electron? I am confused why you use KE to find this out? How do you know when to use KE equation?

Robert
Posts: 144
Joined: Fri Sep 20, 2013 3:00 am

### Re: Kinetic Energy 1.23 c

You would use the kinetic energy formula 1/2 mv^2 because that applies to objects with rest mass. So when you have that energy, add it to the threshold (work function) energy (part b) and then solve for wavelength.

004253593
Posts: 218
Joined: Fri Sep 20, 2013 3:00 am

### Re: Kinetic Energy 1.23 c

how do you know what objects have rest mass?

powerberry
Posts: 108
Joined: Fri Sep 20, 2013 3:00 am

### Re: Kinetic Energy 1.23 c

The rest mass is the mass of a stationary object. In this case, photons do NOT have rest mass, while electrons do.

704628249
Posts: 43
Joined: Fri Sep 25, 2015 3:00 am

### Re: Kinetic Energy 1.23 c

Well, Energy or hv= Work needed to remove an electron + the Kinetic Energy. So you plug in the given information and find out what you need.

Alondra Loera 1A
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

### Re: Kinetic Energy 1.23 c

Just to clarify photons are wave particles and according to special relativity, light is constantly traveling with speed c. Therefore photons are never at rest and do not have a rest mass but because they have energy they do have a mass. Particles such as electrons and protons do have a rest mass .