__Objective__:

The objective of this experiment is to measure the mass of electron by using
electric and magnetic fields**.**

__Equipment__:

A tuning-eye, a * high-voltage dc source*, two

__Theory__:

A set of * perpendicular electric
and magnetic fields* may
be used to measure the

When charge ** q **moving
at speed

**F _{m }**=

The perpendicularity
of F_{m} and v guarantees
a **centripetal force**

that is indeed the magnetic force * F_{m} *itself

Dividing both sides by ** v** and
solving for

If * an electron *of
mass

(1)

The difficult variable to measure in equation **(1)** is
** v**,

P.E. loss = K.E gain

or,

*e*V* **= 0.5Mv ^{ 2}.*

From this equation, ** v^{2} **may
be calculated as

(2)

Solving **(1)** for * v* and
then

(3)

Equating (2) and (3), gives:

Dividing both sides by ** e/M**,

(4)

This equation in which **V** is the * voltage of* the high-voltage
source will be used to solve for

__Procedure__:

A * tuning-eye *is
an electronic device widely used in

The positive dish-like surface is coated with a metal oxide that glows green**/**blue
as electrons hit it**.** A metal cap is placed over the element which is
held by three thin legs**.** These legs cast shadow on the dish, making
straight lines on it when the tuning-eye is in use**.** Increasing **V** makes
the dish glow brighter**.** An instruction comes with each tuning-eye that
must be followed for proper use**.** The following steps should be taken**:**

- Connect the filament wires (as indicated in the instruction) to an
appropriate voltage
**V**_{1}. - Wait a few seconds for the filament to warm up and observe its reddish
color
**.** - Connect the other wires as indicated in the instruction to the second
appropriate source and increase the voltage to the appropriate level
**V**and observe that the dish attains a bluish or greenish color**.**Pay attention to the shadow cast on the dish by the cap's legs and note that they are straight lines as viewed from the top of the tuning eye**.** - Connect a pre-selected
(**solenoid**) to an appropriate power supply that can provide a few amperes**with known number of loops per meter****.**An ammeter must be placed in the solenoid circuit for a more-accurate current measurement**.**that the**Note**must be inserted in its*ammeter positive lead***10-A hole.** - With a current of about
passing through the solenoid, place the solenoid over the tuning-eye tube so that the filament is positioned at the center of it, and observe how the shadows (straight lines) bend as the magnet is lowered**1A****.**The value that you will later on calculate for the**B**of the solenoid in only good for the middle of the solenoid**;**therefore**,**make sure that the filament is precisely inside and at the middle of the solenoid**.** - Adjust the dish voltage
**V**, and the solenoid currentto get a nice curve for the shadow of each leg in the tuning eye**I****.**The radius of curvatureof the curved shadows must be measured**R****.**Anyobject that goes into the solenoid may be used**cylindrical****non-metallic****.**While holding a round and slender object inside the solenoid and looking straight down on to it, try to match the curvature of the shadow with the curvature of that object by adjusting**V**and*I***.** - Try
**three**different round objects and obtain three different sets of**V**,and*I*,*R*. - For each set, calculate
, where**B = μ**_{o}n Iis the**n**of the solenoid**number of****loops per meter****.** -
## Use

*B,*V*,**and*along with*R*to find the value of**e**for each set by using equation**M****(4).** - Find a
using the three calculated values**mean value for M****.**This is your*measured value*.

__Data__:

**Given:****M _{accptd }=
9.11x10^{ -31} kg.**

** n =** number
of loops per meter of the solenoid from its specifications

** μ**

**Measured:****V, *** I, *and

__Calculations__:

Follow the steps under "Procedure**.**"

__ __

__Comparison of the Results__:

The accepted and measured values of * M* may
be used to obtain a % error

__
Conclusion__: To be
explained by students**.**

** Discussion: **
To be explained by students