Electrostatics

Question 1

Why is a charged object able to attract a non charged object?

Answer 1

Because the electric field of the charged object induces a charge in the non charged object by pushing the electrons to the far side leaving a surplus of positive ions on the near side.

Question 2

Explain the principle of static electricity

Answer 2

When two objects are rubbed together then one will scrape electrons of the surface of the other. Thus leaving one object with a positive charge (shortage of electrons) and one with a negative charge (surplus of electrons).

Question 3

Explain magnetic attraction in charged objects

Answer 3

If a charged object is brought near an electrically neutral but conducting object (e.g a piece of aluminium foil) the magnetism of the charged object will push the electrons in the foil to the far side. Thus there is a lack of electrons on the near side and the two objects will attract.

Question 4

Explain a DIY electroscope

Answer 4

Two squares of aluminium foil hanging from a paperclip or piece of wire. If it is brought near a charged object the magnetism from the object will push the electrons to the far side. Thus the near side of both sheets of foil will be positively charged and they will repel visibly.

Question 5

Are insulators or conductors better able to hold static charge and why.

Answer 5

Insulators are better able to hold static charge because in conductive materials the surplus electrons are able to move freely and the charge will bleed away and need constant replenishment (new electrons) to maintain charge. This is why nylon carpets and bedsheets are more prone to creating static shocks.

Question 6

What is the name for a material that can support a sustained electric field with only slow loss of charge?

Answer 6

A Dialectric

Question 7

Describe an electric field created by a DC voltage source

Answer 7

Two metal plates of even size with a small gap between them connected to a DC source. Positive charge will build up on the positive plate (north) with electric field lines flowing to the negative plate (south).

The electric field strength (variable: E) (unit volts per meter, V/m)

will increase with increasing voltage and decrease with increasing distance between the two plates.

Question 8

What is the definition of electric field strength

Answer 8

The force exerted by an electric field on a point charge divided by that charge. The constant unit of charge will have different levels of force exerted upon it depending on the strength of the field that it is inside.
E = F/Q

Q is a unit charge i.e 1 coulomb.
E is electric field strength unit: V/m
F is force in newtons.

Question 9

Explain electrostatic flux

Answer 9

(Unsure of concept revisit later)
Flux has a symbol phi φ
unit of coulombs (q)
It is equal to the charge creating it.

Flux density has a unit of coulombs per meter square.
Q/m²

Question 10

Explain permittivity of a dialectic

Answer 10

(Not confident with concept revisit later)
Permittivity (symbol: epsilon ε)

Is the extent to which a dielectric will give flux density within a given charged field. 
ε=D/E
Thus permittivity (ε) is equal to flux density (D) divided by the strength of the field (E).

Question 11

What happens to a particle if it:
Gains electrons
Loses electrons

Answer 11

Atoms losing electrons become “less negative” so gain a positive charge.
Atoms gaining electrons become “more negative” so gain a negative charge.