Electrostatics Regents Practice

A particle of aluminum is found to have 13 protons in its nucleus with 10 electrons in orbit around the nucleus. This particle would be:

• positively charged

• negatively charged

• electrically neutral

• heavier than a normal aluminum atom

Answer explanation

Electrons are negatively charged; protons are positively charged in the same amount. Because there are more protons than electrons, the aluminum has a net positive charge.

What part of the atom is most likely to be transferred as a body acquires a static electric charge?

• proton

• neutron

• electron

• positron

Answer explanation

Electrons are the charged particles that move; protons and neutrons are bound in atomic nuclei, so they can't get around (and positrons are antimatter and are relatively rare - we'll discuss them in more detail later).

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An object can not have a net charge of: (Hint: consider e)

• 3.2 * 10^-19 C

• 4.5 * 10^-19 C

• 8 * 10 ^ -19 C

• 9.6 * 10^-19 C

Answer explanation

Objects have to gain/lose integer numbers of electrons; 4.5*10^-19 C would represent losing 2.8 electrons, which can't happen! All of the other numbers are multiples of 1.6*10^-19.

Consider the electrons in the pith ball!

• A

• B

• C

• D

Answer explanation

The pith ball will have the charges separate (electrons free the rod). This results in positive charge close to the rod, so the pith ball will move towards the rod.

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• A

• B

• C

• D

A glass rod is given a positive charge by rubbing it with silk. The rod has become positive by:

• Gaining electrons

• Gaining protons

• Losing electrons

• Losing protons

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• A

• B

• C

• D

Answer explanation

The further away from the charge, the less field intensity there is (this is the butter gun!)

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Which diagram best represents the charge distribution on sphere B?

• 
• 
• 
• 

Answer explanation

Sphere A has excess electrons, so it is negatively charged. This causes the electrons in sphere B to push away, towards the right side of sphere B, resulting in positive charge on the left and negative charge on the right.

• A

• B

• C

• D

Answer explanation

Magnetic field lines always leave North poles and enter South poles.

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• an increase in potential energy of the clip

• an increase in the gravitational field strength near the clip

• a decrease in the magnetic properties of the clip

• a decrease in the magnetic field strength near the clip

Answer explanation

As the magnet is lifted, field strength goes down (as an inverse square, butter gun, etc.).

This allows the (constant) force of gravity to exceed the (decreasing) magnetic force upwards, so the paper clip falls.

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