Static Electricity (OCR GCSE Physics A (Gateway))

Electric Forces Between Charges

• The charge of a particle is either:

  • Positive

  • Negative

  • Neutral (no charge)

• Electrons are negatively charged particles, whilst protons are positive and neutrons are neutral

• This is why in a neutral atom, the number of electrons is equal to the number of protons

  • This is so the equal (but opposite) charges cancel out to make the overall charge of the atom zero

The number of negative electrons in an atom balances the number of positive protons

• Therefore, an object becomes negatively charged when it gains electrons and positively charged when it loses electrons

• When two charged particles or objects are close together, they also exert a force on each other

• This force could be:

  • Attractive (the objects get closer together)

  • Repulsive (the objects move further apart)

• Whether two objects attract or repel depends on their charge

  • If the charges are the opposite, they will attract

  • If the charges are the same, they will repel

Opposite charges attract, like charges repel

Attraction or Repulsion Summary Table

• Attraction and repulsion between two charged objects are examples of a non-contact force

  • This is a force that acts on an object without being physically in contact with it

Static Electricity

• Common electrostatic phenomena include:

  • Shocks from everyday objects

  • Lightning

  • A charged balloon sticking to a wall

  • Charged comb picking up small pieces of paper

Shocks From Everyday Objects

• The build-up of electrostatic charge can be quite dangerous and can cause sparking (also known as an electric shock)

• A static electric spark occurs when:

  • Two objects are charged by friction

  • They become oppositely charged

  • The large surplus of electrons causes electrons to 'jump' across to an object that is neutral

• Since a current is the flow of electrons, this causes a small current to flow between the objects, called a spark

• An example of sparking is the small electric shock felt from touching a door handle, or another person, after walking on a vinyl floor or nylon carpet with rubber shoes or socks

  • Sparks can become quite dangerous and can cause a fire by igniting flammable gases and liquids, such as petrol

    

Examples of sparking from touching a door handle or another person

Lightning

• In a storm, clouds move over each other

  • This causes them to become charged when electrons are transferred between them

• Since the ground is neutral, the negative charges from the cloud jump to meet the positive charges on the ground creating a giant spark (a current from a transfer of charge)

  • This phenomenon is known as lightning

Lightning is caused by the build-up of charge in clouds

Sticking a Balloon to the Wall

• Rubbing a balloon on a woollen jumper transfers electrons onto the balloon by friction

• The balloon is now negatively charged whilst the jumper is left positively charged

• The wall is still neutral, however, when the balloon is placed near the wall, the positive charges in the wall are brought to the surface because they are attracted to the negative charge of the balloon

• Since opposite charges attract, the balloon sticks to the wall from only the electrostatic attraction

Charged Comb Picking up Paper

• Static electricity can be observed when running a plastic comb through hair then placing the comb near small pieces of paper

  • The pieces of paper can be observed to jump up and stick to the comb

• The comb becomes charged by friction from the hair so it is left with a negative charge as the electrons are transferred to it

  • This also means the hair strands become positively charged and they begin to repel each other

• Pieces of paper are neutral but as the comb comes close to them, the positive charges are brought to the surface of the paper and are attracted to the negative charges on the comb

  • Therefore, the papers 'stick' to the comb through static electricity

A negatively charged comb can attract small pieces of paper