P4 a-d Flashcards
Name two types of charge.
Positive and negative
Like charges always…….
Like charges always repel, opposite charges attract.
What charge do all electrons have?
Electrons are always negative.
There is no such thing as a positive electron!
How can you get an electric shock?
If you touch something that is charged.
When can static electricity be a nuisance?
TV screens and computer monitors gather dust, clothes cling to you, getting electric shocks in supermarkets.
When can static electricity be dangerous?
When near fuels, e.g. when refuelling a plane or at a petrol station.
How do we use static to remove smoke from chimneys?
- Smoke passes through a metal grid at high voltage.
- This charges the smoke particles.
- They are attracted to oppositely charged plates above the grid.
- This stops the smoke particles going into the air.
- The particles fall back down the chimney and are collected as ash.
Explain why a circuit with a break in it will not work?
The electrons can not move around the circuit so it is incomplete.
When can static electricity be useful?
Heart defibrillators, photcopiers, smoke precipitators, spray painting vehicles.
Explain why plugs are made of rigid plastic.
So they don’t conduct electricity.
What does a fuse wire do when too much current flows through it?
The fuse melts or blows. (NOT blows up!!!)
List three wires found in a UK plug.
Earth, Live, Neutral
What colour is the live wire?
Brown
What colour is the earth wire?
The Earth wire is yellow/green.
What colour is the neutral wire?
The neutral wire is blue.
What happens to the resistance if a longer wire is used?
Resistance increases if the wire is longer (the electrons have more atoms to get past, so there are more collisions which slow the electrons down).
What is the unit of resistance?
Resistance is measured in Ohms.
What does an earth wire do?
The earth wire allows electrons to flow back to earth safely if the live wire comes loose and touches the metal case. The high current flowing back to earth melts the fuse so the circuit switches off.
Describe how to measure the wavelength of a longitudinal wave.
Measure from one area of compressions to another area.
What type of substances build static electricity?
Insulators - because the elctricity can’t flow througth an insulator which is why it’s called static!
What is a defibrillator?
It is a machine used to restart a person’s heart after it has stopped.
Why are the paddles on a defibrilator insulated?
So the person holding them does not get an electric shock.
Name a use for ultrasound.
Baby scans, looking at body organs such as the liver and breaking up kidney stones.
What property of ultrasound waves allows them to penetrate inside the body?
They are high frequency and have a short wavelength.
What are the positive charges called?
Protons
Which charges can move and which can not?
Electrons can move, protons can not.
Describe how an acetate rod becomes charged when you rub it with a cloth.
When an acetate rod is rubbed with a woollen cloth, electrons move from the acetate rod onto the cloth. The acetate rod becomes positively charged, as it has lost negatively charged electrons. the cloth will be negatively charged as it gains electrons.
If the length of a wire is increased, what happens to the current?
The current is reduced because the resistance will have gone up as the wire is longer.
What are the areas of high pressure in a longitudinal wave called?
Compressions
What are the areas of low pressure called in a longitudinal wave?
Rarefactions
Why is ultrasound used instead of x-rays in baby scans?
Ultrasound is used instead of xrays in baby scans becuase x-rays can damage living cells and so could damage the fetus.
Also, x-rays go straight through soft tissues, so would only show the bones.
What does double insulated mean?
Double insulated appliances have plastic cases without any wires connected to the case. This means the case cannot become live because plastic does not conduct electricity.
What is ultrasound?
Sound waves with a frequency greater than 20000Hz which humans cant hear.
Explain how ultrasound can be used to produce a picture of an unborn baby.
Ultrasound reflects from boundaries between different tissues. The computer uses the time taken for these reflections.
Explain the advantages of using static electricity to spray paint cars.
The advantages are that the spray paint all has the same charge, so it repels making a fine spray.
Also, the car is the opposite charge to the paint meaning the paint is attracted to it.
This makes it easier to paint odd shaped objects and wastes less paint.
