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### Kinetic Energy 1.23 c

Posted: Sat Oct 12, 2013 3:10 pm
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?

### Re: Kinetic Energy 1.23 c

Posted: Sat Oct 12, 2013 3:20 pm
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.

### Re: Kinetic Energy 1.23 c

Posted: Sun Oct 13, 2013 3:44 pm
how do you know what objects have rest mass?

### Re: Kinetic Energy 1.23 c

Posted: Sun Oct 13, 2013 10:42 pm
The rest mass is the mass of a stationary object. In this case, photons do NOT have rest mass, while electrons do.

### Re: Kinetic Energy 1.23 c

Posted: Wed Dec 02, 2015 6:35 pm
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.

### Re: Kinetic Energy 1.23 c

Posted: Thu Dec 03, 2015 10:49 pm
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 .