Part 1: In 1909 Robert Millikan was the first to find the charge of an electron in his now-famous oil drop experiment. In the experiment tiny oil drops are sprayed into a uniform electric field between a horizontal pair of oppositely charged plates. The drops are observed with a magnifying eyepiece, and the electric field is adjusted so that the upward force q E on some negatively charged oil drops is just sufficient to balance the downward force m g of gravity. Millikan accurately measured the charges on many oil drops and found the values to be whole-number multiples of 1.6 × 10−19 C — the charge of the electron. For this he won the Nobel Prize. If a drop of mass 1.82857 × 10−13 kg remains stationary in an electric field of 7 × 105 N/C, what is the charge on this drop? The acceleration due to gravity is 9.8 m/s 2. Answer in units of C. Part 2: How many extra electrons are on this particular oil drop (given the presently known charge of the electron)?
Part 1: In 1909 Robert Millikan was the first to find
the charge of an electron in his now-famous
oil drop experiment. In the experiment tiny
oil drops are sprayed into a uniform electric
field between a horizontal pair of oppositely
charged plates. The drops are observed with
a magnifying eyepiece, and the electric field is
adjusted so that the upward force q E on some
negatively charged oil drops is just sufficient
to balance the downward force m g of gravity.
Millikan accurately measured the charges on
many oil drops and found the values to be
whole-number multiples of 1.6 × 10−19 C —
the charge of the electron. For this he won
the Nobel Prize.
If a drop of mass 1.82857 × 10−13 kg
remains stationary in an electric field of
7 × 105 N/C, what is the charge on this drop?
The acceleration due to gravity is 9.8 m/s 2.
Answer in units of C.
Part 2: How many extra electrons are on this particular oil drop (given the presently known charge
of the electron)?
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