Lesson test: Charge and Coulomb's law

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Charge and Coulomb's law

1.[2p]
Why does every circuit diagram show conventional current flowing opposite to the actual motion of the electrons?

Franklin guessed which way his single fluid flowed and got it backwards, and the convention stuck

Correct

Electrons move backwards inside a conductor but forwards outside it

The answer is: Franklin guessed which way his single fluid flowed and got it backwards, and the convention stuck

The convention was chosen so that Coulomb's law would come out positive

The answer is: Franklin guessed which way his single fluid flowed and got it backwards, and the convention stuck

Positive charge really does flow in a metal, alongside the electrons

The answer is: Franklin guessed which way his single fluid flowed and got it backwards, and the convention stuck

2.[2p]
Two point charges of $+ 4.0$ μC and $- 6.0$ μC sit 30 cm apart. What is the magnitude of the force between them, in newtons?

CorrectNot quite: 2.40

3.[3p]
Coulomb's third data point, at a separation of 8.5 degrees, came out about 11 per cent below what an inverse square predicts. What is the honest thing to say about it?

He attributed it to charge leaking from the balls during the reading, and the law is trusted today because of far more sensitive null experiments

Correct

The discrepancy shows the exponent is really about 2.06

The answer is: He attributed it to charge leaking from the balls during the reading, and the law is trusted today because of far more sensitive null experiments

The point was fabricated, as later analysis proved

The answer is: He attributed it to charge leaking from the balls during the reading, and the law is trusted today because of far more sensitive null experiments

An 11 per cent error is within the expected scatter of any measurement

The answer is: He attributed it to charge leaking from the balls during the reading, and the law is trusted today because of far more sensitive null experiments

4.[2p]
The ratio of the electric to the gravitational force between a proton and an electron depends on how far apart they are.

True

The answer is: False

False

Correct

5.[3p]
Which of these are experimental facts rather than deductions from Coulomb's law?

Select all that apply

Charge is conserved in every process ever observed

Correct

Free charge comes only in integer multiples of $e$

Correct

Forces from several charges add as vectors, with no screening

Correct

The force between two charges obeys Newton's third law

The answer is: Charge is conserved in every process ever observed, Free charge comes only in integer multiples of $e$, Forces from several charges add as vectors, with no screening

6.[3p]
Charges $q_{1} = + 5.0$ nC at $x = 0$ and $q_{3} = - 8.0$ nC at $x = 10.0$ cm act on $q_{2} = + 3.0$ nC at $x = 4.0$ cm. What is the magnitude of the net force on $q_{2}$ , in micronewtons?

CorrectNot quite: 144

7.[3p]
Two positive charges, $+ 9.0$ μC and $+ 1.0$ μC, are fixed 2.00 m apart. How far from the larger charge, in metres, is the point between them where a test charge feels no net force?

CorrectNot quite: 1.50

8.[2p]
Astronomy is governed by gravity rather than by electricity because

charge has two signs, so any large accumulation attracts its own neutraliser

Correct

gravity is the stronger of the two forces at astronomical distances

The answer is: charge has two signs, so any large accumulation attracts its own neutraliser

the electric force falls off faster than the inverse square at long range

The answer is: charge has two signs, so any large accumulation attracts its own neutraliser

stars are made of neutrons, which carry no charge

The answer is: charge has two signs, so any large accumulation attracts its own neutraliser

9.[3p]
Match each experimenter to what they established.

Gray
du Fay
Millikan
Cavendish

charge comes in multiples of one unit
no charge sits inside a closed conductor
electricity can be conducted along a thread
there are two kinds of charge

Show the answer

Gray: electricity can be conducted along a thread du Fay: there are two kinds of charge Millikan: charge comes in multiples of one unit Cavendish: no charge sits inside a closed conductor

1.[2p] Why does every circuit diagram show conventional current flowing opposite to the actual motion of the electrons?

2.[2p] Two point charges of +4.0 μC and -6.0 μC sit 30 cm apart. What is the magnitude of the force between them, in newtons?

3.[3p] Coulomb's third data point, at a separation of 8.5 degrees, came out about 11 per cent below what an inverse square predicts. What is the honest thing to say about it?

4.[2p] The ratio of the electric to the gravitational force between a proton and an electron depends on how far apart they are.

5.[3p] Which of these are experimental facts rather than deductions from Coulomb's law?

6.[3p] Charges q1=+5.0 nC at x=0 and q3=-8.0 nC at x=10.0 cm act on q2=+3.0 nC at x=4.0 cm. What is the magnitude of the net force on q2, in micronewtons?

7.[3p] Two positive charges, +9.0 μC and +1.0 μC, are fixed 2.00 m apart. How far from the larger charge, in metres, is the point between them where a test charge feels no net force?

8.[2p] Astronomy is governed by gravity rather than by electricity because

9.[3p] Match each experimenter to what they established.

1.[2p]
Why does every circuit diagram show conventional current flowing opposite to the actual motion of the electrons?

2.[2p]
Two point charges of $+ 4.0$ μC and $- 6.0$ μC sit 30 cm apart. What is the magnitude of the force between them, in newtons?

3.[3p]
Coulomb's third data point, at a separation of 8.5 degrees, came out about 11 per cent below what an inverse square predicts. What is the honest thing to say about it?

4.[2p]
The ratio of the electric to the gravitational force between a proton and an electron depends on how far apart they are.

5.[3p]
Which of these are experimental facts rather than deductions from Coulomb's law?

6.[3p]
Charges $q_{1} = + 5.0$ nC at $x = 0$ and $q_{3} = - 8.0$ nC at $x = 10.0$ cm act on $q_{2} = + 3.0$ nC at $x = 4.0$ cm. What is the magnitude of the net force on $q_{2}$ , in micronewtons?

7.[3p]
Two positive charges, $+ 9.0$ μC and $+ 1.0$ μC, are fixed 2.00 m apart. How far from the larger charge, in metres, is the point between them where a test charge feels no net force?

8.[2p]
Astronomy is governed by gravity rather than by electricity because

9.[3p]
Match each experimenter to what they established.