Modern Physics
Modern Physics
3rd Edition
ISBN: 9781111794378
Author: Raymond A. Serway, Clement J. Moses, Curt A. Moyer
Publisher: Cengage Learning
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Question
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Chapter 4, Problem 6P

(a)

To determine

The radius and the mass of the drop used in the experiment.

(a)

Expert Solution
Check Mark

Answer to Problem 6P

The radius is 1.62×106m_ and the mass is 1.42×1014kg_.

Explanation of Solution

Write the expression for the radius of the oil drop in the Millikan’s experiment.

    a=9ηv2ρg        (I)

Here, η is the viscosity of the liquid, v is the velocity of the oil drop, ρ is the density and g is the acceleration due to gravity.

The mass of the oil drop is given by,

    m=ρV        (II)

Here, V is the volume, m is the mass of the oil drop.

The volume of the oil drop is given by,

    V=43πa3        (III)

Use equation (III) in (II),

    m=ρ(43)πa3        (IV)

The average speed of the oil drop is given as,

    v=ΔyΔt=4.0×103m15.9s=2.52×104m/s

Conclusion:

Substitute 1.81×105kg/ms for η, 2.52×104m/s for v, 800kg/m3 for ρ and 9.81m/s2 for g in equation (I) to find a.

    a=(9(1.81×105kg/ms)(2.52×104m/s)2(800kg/m3)(9.81m/s2))1/2=1.62×106m

Substitute 1.33 for ρ, 1.62×106m for a in equation (IV) to find m.

    m=(1.33)(800kg/m3)(π)(1.62×106m)3=1.42×1014kg

Therefore, the radius is 1.62×106m_ and the mass is 1.42×1014kg_.

(b)

To determine

The charge on each drop and show that the charge is quantized by considering both the size of each charge and the amount of charge gained when the rise time changes.

(b)

Expert Solution
Check Mark

Answer to Problem 6P

It is shown that the charge is quantized by considering both the size of each charge and the amount of charge gained when the rise time changes.

Explanation of Solution

The charge on the droplet is given by,

    q1=mgE(v+v1)v        (V)

Here, v is the velocity of fall, v is the velocity of rise, E is the electric field, v is the upward terminal speed in the presence of the electric field, v is the downward terminal velocity in the absence of the electric field.

The expression for the electric field is given by,

    E=Vd        (VI)

Conclusion:

Using the times given, the various v can be calculated as,

    v1=4×103m36.0s=1.11×104m/sv2=4×103m17.3s=2.31×104m/s

    v3=4×103m24.0s=1.67×104m/sv4=4×103m11.4s=3.51×104m/s

    v5=4×103m7.54s=5.31×104m/s

The corresponding charges can be written as,

    q1=(6.97×1019C)(2.52+1.11)2.52=10.0×1019Cq2=13.4×1019C

    q3=11.6×1019Cq4=16.7×1019Cq5=21.6×1019C

Therefore, It is shown that the charge is quantized by considering both the size of each charge and the amount of charge gained when the rise time changes.

(c)

To determine

The electronic charge from the data.

(c)

Expert Solution
Check Mark

Answer to Problem 6P

The average value is 1.67×1019C_.

Explanation of Solution

To find an integer n1 such that 1.5×1019<qn1<2.0×1019

    q16=1.67×1019Cq28=1.68×1019Cq37=1.66×1019Cq410=1.67×1019C

  q513=1.66×1019C

The amount of charge gained or lost is,

    q2q1=3.4×1019Cq3q1=1.6×1019Cq2q3=1.8×1019Cq4q1=6.7×1019C

    q4q3=5.1×1019Cq4q2=3.4×1019Cq5q1=11.6×1019Cq5q4=4.9×1019C

    q5q4=4.9×1019Cq5q3=10.0×1019C

The integers that yield a value of e between 1.5 and 2.0×1019C.

    q2q12=1.70×1019Cq3q11=1.60×1019Cq2q31=1.80×1019Cq4q14=1.68×1019C

    q4q33=1.70×1019Cq4q22=1.65×1019Cq5q17=1.66×1019Cq5q43=1.63×1019C

    q5q36=1.67×1019C

The average of all values will be 1.67×1019C.

Conclusion:

Therefore, The average value is 1.67×1019C_.

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