Chapter 16 - Static Electricity Flashcards
What are the 3 possibilities that an objects can be in?
Neutral
Positively-charged
Negatively-charged
What are the 2 FACTS for charges in this chapter?
Only NEGATIVE charges can move freely
Charges can NEVER be destroyed in the process of rubbing.
What happen when a neutral polythene strip rub against a neutral wool
The negative charges of the neutral wool will be separated from the positive charges and transfer to the polythene strip. As a result, there will be excess positive charges at the wool and wool become positively charged and there will be excess negative charges on the polythene strip and it becomes negatively charged.
What is the S.I Unit for Charges
Coulomb (C)
1 Coulomb = How many charges
6.25 x 10^18
Examples of electrical insulators
Glass, wool, silk
Examples of electrical condutors
Copper, Iron, steel
What is a electrical conductor means?
It meas that the material do allow electric charges to flow through them easily
Whether a object is a electrical conductor is depends on ______ ________.
Atomic Structure
What are the three methods you can use to charge a object?
Charging by friction
Charging by induction
Charging by contact
Using one rod, TWO spheres, how can we obtain opposite charges on two conductors by induction
Name the two spheres as Y and Z.
Y and Z is touching each other, side by side
Choose a negatively/positively charged rod
For Positively charged rod,
Place the positively charged rod near to Y, but not touching.
The negative charges on Y and Z will be induced to the left sides of the Y.
Move away Z, Z will then be positively charged due to the excess amount of positive charges presented
Move away the rod, Y will be negatively charged due to the excess amount of negative charges presented
Using one rod, ONE sphere, and a wire, how can we obtain a opposite charges on a single sphere by induction?
Choose Negatively/Positively Charged rod
For Negatively Charged rod,
Place the rod near to the sphere, but not touching.
The negative charges will be separated from the positive charges on the sphere and they will be induced to the right end of the sphere.
Connect a wire to the sphere, the negative charges will transfer from the sphere to the earth. (This process is called earthing)
Remove wire
Remove the Negatively charged rod
The excess amount of positive charges make the sphere to be positively-charged.
Why a charged object can pick small pieces of paper? Use the positively charged rod and a small piece of neutral paper to explain?
When the positively charged rod is brought near to the piece of paper. The negative charges of the paper is INDUCED to the end nearer to the rod. When the rod touches the paper, the negative charges is transferred to the rod to neutralize some of the positive charges of the rod. The paper then become positively charged due to the excess amount of positive charges presented. As like charges repels, the paper eventually moves away from te rod.
To neutralize a charged body is to remove _______
excess charges from it
In this chapter, Neutralisation is also called ______
Discharging
What are the two ways to neutralise a charged body?
ADD Negative charges or REMOVE excess charges
How to discharge a positively charged glass (insulator) rod? Two ways and explain
1ST WAY
Put the glass rod in a damp condition. Damp condition means that the amount of water molecules present in that area is high. The neutral water molecules will move around randomly and come in contact with the positively charged glass rod. The negative charges on the water molecules will transfer over to the glass rod and neutralise the positive charges on the glass rod.
2ND WAY
Put the glass rod on top of a burning candle, directly above the flame. The flame will give out intensive heat which will ionise the nearby air particles. The neutral air molecules are separated into postively charged molecule and negatively charged molecules. The negative charged molecules will come in contact with the rod and the negative charges will transfer to the rod to neutralise the positive charges.
Define electric field
An electric field is a region in which a electric charge experience an electric force
In the drawing of electric field diagram, we always draw electrical line that represents the path of a _______ charge
Positive
The CLOSER the field line, the ______ is the electric field strength in that region
Stronger
How to neutralise a charged conductor?
Earthing, connect a wire to the conductor.
NEGATIVE charges is either transfer from the earth to the conductor or transfer from the conductor to the earth
What is the direction of the electric force for a positive charge
Outwards from the middle
What is the direction of the electric force for a negative charge
Inwards to the middle
How a photocopy-machine works? 6 Steps!
- Inside the machine, there is a drum coated with selenium which is a special semi-conductor that conduct charges when there is light.
- The drum is rotated near a highly-charged wire in order to be positively charged.
- An intense beam of light shine on the paper that needs to be photocopied. The light is then reflected by the paper to the drum. The image on the paper will reflect lesser light as it appears to be a darker area. The part where the drum experience lesser light will be remain charged while the part where the drum experience intensive light will be discharged.
- Toners are sprayed onto the charged spot of the drum and since the toners and the charged part of the drum is of opposite charges, the toners will be induced to the charged part of the drum but it will not neutralise the charges on that part of the drum.
- The drum is then roll over against a new positively/negatively charged paper and the toners which is of the opposite charges will be transferred to the new paper.
- The new paper is heated to ‘fix’ the toners onto it.
Another application of electrostatic other than photocopy machine
Spray Painting
Example of hazards of electrostatics
Petrol tanker and aeroplane
Friction between lorry and air as the lorry travels can build up an electric charge.
A Spark from this electric charge can cause petrol vapour to explode
To prevent this, a metal chain from the lorry to the ground is provided for the charge to escape to the earth
Lightning is an other example
