Saturday
May 25, 2013

# Homework Help: Physics

Posted by ALan on Monday, December 7, 2009 at 10:51pm.

A cathode ray tube operates at 80 kV with a current of 875 uA. Calculate the
a)Intesity (# of photons per second f the x-rays
b)Minimum wavelength of the x-rays produced by the CRT

• Physics - drwls, Monday, December 7, 2009 at 11:37pm

a) To my knowledge each CRT electron does not necessarily produce 1 X-ray photon. The question cannot be answered with the information given

b) The X-ray photon can have no more energy that the electron striking the cathode, and you know what that is:
E = e*V = 80,000 V * 1.6*10-19 J/V

Use that energy and E > hc/(wavelength) to get the minimum wavelength.

• Physics - ALan, Tuesday, December 8, 2009 at 12:04am

I typed exactly what is said on the question sheet.
As each photon strikes the electron, it is absorbed and then any excess energy is then re-radiated in the form of x-rays, from what i understand, i need to find the remaining energy (since i know energy of electron after using current, t=1.0s and q(charge)=1.60*10^-19c)
And intensity can be figured out by using
E=nhf
E=n(#of photons)h(planks constant, i think its the J per s[6.63*10^-34J.s])f frequencey (which i don't have, this is where im stuck)
My classmate figured it out and I will attempt to retrieve the procedure from him, thanks anyway.

• Physics - drwls, Tuesday, December 8, 2009 at 12:41am

In a CRT, photons do not strike electrons to produce X-rays. Electrons strike metal atoms to liberate photons. The deceleration/excitation process produces both continuum and atomic line radiation. There can be more one photon produced per electron.

Getting agreement with 'book' or 'question sheet' answers does not always mean the book is right, or that the course is being properly taught.

• Physics - ALan, Tuesday, December 8, 2009 at 4:23pm

huh....

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