4.2.5.1 Static Charge

Question 1

What happens when two insulating materials are rubbed against each other?

Answer 1

• both become electrically charged
• negatively charged electrons are rubbed off one material and on to the other - transfer of electrons caused by friction between the 2 materials
• the material that gains electron becomes negatively charged
• the material that loses electrons is left with an equal positive charge

Question 2

When two electrically charged objects are brought closer together:

Answer 2

• they exert a non-contact force on each other
• two objects that carry the same type of charge repel
• two objects that carry different types of charge attract
• attraction and repulsion between two electrically charged objects are examples of non-contacts force

Question 3

Electrical conductor:

Answer 3

a material that allows electrical charge to easily move through it

Question 4

Electrical insulator:

Answer 4

a material does not allow electrical charge to easily move through it

Question 5

What does friction lead to?

Answer 5

electron transfer

Question 6

What do opposite charges do?

Answer 6

attract

Question 7

What do like charges do?

Answer 7

repel

Question 8

What do electrically charged objects exert on another electrically charged object?

Answer 8

exert a non-contact force

Question 9

How to get rods to attract each other:

Answer 9

• bath rods must have different numbers of electrons
• can be achieved by friction
• electrons transfer from one rod to the other

Question 10

How an uncharged object become positively charged:

Answer 10

Negatively charged electrons transfer from the neutral object by friction making it positively charged.

Question 11

What type of charge is always transferred?

Answer 11

always negative charges (electrons) that transfer, never positive charges

Question 12

Van de Graff Generator

Answer 12

• used to generate static electricity
• the longer the Van de Graff generator is switched on, the more charge is stored in the metal dome
• the amount of charge on the metal dome is increased, which causes the potential difference between the metal dome and. the earthed sphere to increase

Question 13

Why does the rod attract the foil (rod has a negative electric charge and foil has a positive electric charge)?

Answer 13

The rod became charged when rubbed with a cloth due to friction causing negative electrons to transfer to the rod from the surface of the cloth. The excess electrons on the rod give it a negative charge.

Question 14

Why does the rod move towards the foil (rod has a negative electric charge and foil has a positive electric charge)?

Answer 14

The foil sticks to a negatively charged cloth as when the rod is moved towards the foil the negative charges move to then end further away from the rod as they repel from the negatively charged rod. The side further away from the rod is negatively charged and the (opposite) side closer to the rod is positively charged. The positive side of the foil is attracted to the negatively charged rod.

Question 15

What is the production of static electricity/sparks caused by?

Answer 15

• by rubbing surfaces which transfers negative charges (electrons) from one insulator to another
• this means they have equal opposite charges as electrons are transferred
• causes a build up of charge → creating a p.d. → sparks

Question 16

Why is metal a good electric conductor?

Answer 16

• because electrons can flow easily through the metals
• they have free electrons
• unlike insulators

Question 17

Why do objects like plastic not conduct electricity?

Answer 17

• they are insulators

- electrons cannot move through insulators

Question 18

Why does a person’s hair stand up when they touch a Van de Graff generator?

Answer 18

• in the regenerator is a moving belt
• as the belt moves the electrons pass from the top plastic roller onto the belt
• electrons pass off the belt and are transferred to earth
• so over time the top region of the generator becomes charged
• the positive charge builds up on the metal dome
• if your are touching the dome you will also have a positive charge as the negative electrons are transferred to the generator to earth
• so the person Ould have an overall positive charge like the metal dome and as like charges repel the persons hair would stand up repelling from the metal dome

Question 19

How can electric fields be used to explain why static charges create sparks.

Answer 19

• Stronger electric fields means some electrons are removed from the air
• causes air to become much more conductive meaning current can easily flow through it
• results in sparks

Question 20

What is earthing?

Answer 20

• when the charge on an isolated object increases
• the p.d. between the object and the Earth increases
• path from high potential to 0V for charge to flow → creating a current

Question 21

What does how close together the field lines show?

Answer 21

the closer together the field lines are the stronger the electric field

Question 22

Why would a negatively charged person get an electric shock if they touched a metal object?

Answer 22

• there is p.d. between the student and the tap
• due to their p.d. the excess electrons transfer from the student to the metal tap which earths the charge
• electric current flows through the person giving them a shock