Prelab - Measurement of e/m             Name:

 

  1. What is the value (SI units)

a.  e, charge on an electron?

 

          b.  m, mass of an electron?

 

          c.  calculate e / m

 

 

 

 

  1. (˝) How are we able to see the path of the moving electrons? 

 

 

 

 

 

 

3.    The magnetic field of the Ealing apparatus is B = 7.8 x 10-4 * I.  Show work for basic units (mks & C) for the numeric constant.  (Hints:  N = kg m/s2 and F = evB)

 

 

 

 

 

 
  1. a.  In our lab, an electron beam is emitted from a heated filament, called a(n) _______, & moves toward the _______ and follows a circular path.

b.  What is the direction of the related Force that causes this circular path?

(Hint: one-word answer is the best.)

 
  1.  (1 ˝) In step 5, we plot V vs r2 to find e/m  The slope ((DV / Dr2) of this graph is equal to ____ ?          (An expression)

 

 

 

 

  1. (BONUS)  This student’s data was measured at 2.0 Amps

diameter

voltage

r2 (x10-3 m2)

6.2 cm

200 V

 

6.8 cm

235 V

 

7.2 cm

270 V

 

7.6 cm

290 V

 

8.0 cm

330 V

 

Please calculate e/m using the results from your graph to the right.

 

Link to Anode/Cathlode in Ealing apparatus

Link to Magnetic field going in the board

Note:  Tip of arrow towards you “out of the board”, or fletching away from you “into the board”

 

(Note: ON a Pre-lab:  If data points fall on the best fit line, you can use data points as slope points.)

                               radius2  (x 10-3 m2)