Answer 8_2_5
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In an experiment to determine the charge on a charged oil droplet, the droplet was held stationary in a vertical electric field of strength 57 kV m-1. After the field was switched off, the droplet fell at a steady speed, taking 18.3 s to fall through a vertical distance of 2.0 mm Viscosity of air = 1.8 × 10-5 N s m-2 Density of oil = 970 kg m-3 g
= 10 m/s-2 (a) Calculate the speed of the droplet as it falls. (b) Show that the droplet’s radius is 9.7 ´ 10-7 m (c) Calculate the charge of the droplet. (d) Compare this to the electronic charge. What does it suggest? |
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(a)
Speed = 2.0 ´ 10-3 ¸
18 = 1.11 ´
10-4 m/s (P) |
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(b)
r2 = 9hv (PP) = 9 ´
1.8 ´
10-5 ´
1.1 ´
10-4
= 9.37 ´
10-13 m2 (P) |
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2rg
2 ´
970 ´
9.8 |
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r
= 9.7 ´
10-7 m |
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(c)
Find out the mass |
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Mass
= 4/3 ´
p
´
(9.7 ´
10-7m)3 ´
970 kg m-3 = 3.69 ´ 10-15 kg (P) |
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Weight
= 3.69 ´
10-15 kg ´ 9.8 m/s2 = 3.61 ´
10-14 N |
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F
= Eq = weight |
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57000
N C-1 ´ q = 3.61 ´ 10-14 (P) |
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q
= 6.37 ´
10-19 C (P) |
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(d)
This is about 4 times the electronic charge.
(P) |
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It
tells us the charge is quantised (goes up in whole number multiples) (P) |
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