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1. A. Which of these correctly gives the gravitational potential felt by a test

ID: 1652831 • Letter: 1

Question

1. A. Which of these correctly gives the gravitational potential felt by a test mass m from a source mass M at a distance r?

a.) +GM/r b.) -GmM/r^2 c.) -GmM/r d.) -GM/r

B. There are two equivalent units for measuring electric field. One is obvious from its definition in terms of Coulomb's law such that F = q E where the force is given by the product of the test charge and the field. The other comes from considering energy when a charge is moved in a field. It is

a.) ampere-second b.) coulomb/meter c.) volt/meter or V/m d.) joules or J

C. If you encountered a very very small charge on something like a tiny speck of dust, what is the smallest magnitude of non-zero charge you could ever find?

a.) +/- 1.6x10^-19C b.) There is no lower limit, Charge is infinitely divisble c.) +/- 1C d. ) +/- 10^-9C, a nanocoulomb

Explanation / Answer

A)

Gravitational Potential : V = -GM/r <----- option (d)

It is negative because, gravitational force is attractive in nature

B)

Answer: Volt/meter (c)

Voltage , V = E*d <---- E = electric field, d = displacement

So, E = V/d

So, unit of E = volt / meter

C)

Answer : +/- 1.6*10^-19 C (a)

Smallest unit of charge is electronic / protonic charge whose value is 1.6*10^-19 C