Electric charge Book page 66 69 Syllabus 2.19 2.23 16/3/2016 Lightening cgrahamphysics.com 2016
Test your knowledge Where is the lightning capital of the world? What should you do when you hear thunder? Where is a safe place when you are outside? A) in a car B)in the middle of a field C)In a house D) Lying face down on the ground Using a telephone during a lightening storm is dangerous A) true B) false On average the number of people who die in the USA each year from lightning is about A) 10 B) 100 C) 1000 D) 100000 The greatest number of people who die from being struck by lightning are A) Golfers B) Fishermen C) Farmers D) Joggers What is the longest recoded lightening bolt? A) 9km B) 19km C)190km D)900km What causes lightning and thunder? The Birth of a Lightning Bolt.mp4
Starter Link the words: Current Watts (W) Voltage Amps (A) Power Volts (V)
Aim Identify common materials which are electrical conductors or insulators, including metals and plastics. Explain how insulating materials can be charged by friction. Recall that there are forces of attraction between unlike charges and forces of repulsion between like charges. Keywords Conductor Insulator Charge Electroscope Electrostatic
Where does lightning come from Have you ever wondered The bigger picture 16/3/2016 cgrahamphysics.com 2016
Find the link What do the following familiar events have in common? A lightning strike. Dusters that attract dust. Crackles when combing hair. Cling film sticking to your hands. Dust being attracted to television screens. Clothes clinging to each other in a dryer. Getting a shock after rubbing your feet on a carpet and then touching a metal object. All these events are due to static electricity.
What is static electricity? Static electricity is due to the build-up of electric charge. It is called static electricity because the charge is unable to flow. The build-up of electric charge can cause dangerous sparks. Sometimes, after walking on a carpet and then touching a metal object, such as a door handle, you might get a small shock. This is caused by static electricity.
Charges within the atom A neutral atom is made up of three particles: proton neutron electron positive negative The electron is negative because it must do all the moving The proton is stuck. It cannot change its place 16/3/2016 cgrahamphysics.com 2016
Moving electrons A neutral atom has the same number of protons and electrons this makes it neutral! The neutral atom can lose an electron what will happen to the number of protons and electrons? What will its charge now be? It now has more protons than electrons, making it a positive ion
continued The neutral atom can gain an electron what will happen to the number of protons and electrons now? What will its charge be? It now has more electrons than protons, making it a negative ion Gain an 16/3/2016 cgrahamphysics.com 2016 Negative
Opposite charge attract Like charge repel
Conductors and insulators Some materials are good electrical conductors Materials that do not allow electrons to move freely are called electrical insulators
If an uncharged balloon is rubbed against hair, the electrons will move onto the balloon This will cause the hair to be left with no electrons it will be positive The balloon will now have more electrons it will be negative
Charging by friction Rubbing two different materials together creates a separation of charge This means that electrons can move from one object to another The rubber rod becomes negatively charged because it has gained an excess of electrons The fur becomes positively charged because it has a deficit of electrons
The balloon is negatively charged and induces 16/3/2016 a positive charge in cgrahamphysics.com the wall 2016
Let s rip Can you rip/tear/cut the pieces of paper into the SMALLEST pieces possible please? Rub a plastic comb on your sweater Try to pick up as many paper pieces as you can. The comb induces a charge in the paper, the two attract Can you explain what cgrahamphysics.com is happening? 2016 16/3/2016
Bending water Can you explain what is happening? The balloon has gained excess electrons and is negatively charged The negative charge attracts the positive water molecules and repels the negative charged The water stream bends toward the balloon as like charges attract cgrahamphysics.com 2016 16/3/2016
A charged object is brought close to the metal plate on top
This attracts the negative charges towards the metal plate The gold leaf and the rod are left with a positive charge and repel If the object is moved away, the electron will re-distribute and the gold leaf will fall How could you give it a permanent negative charge? The electroscope is earthed by touching it This will attract negative charges from Earth through the hand onto the electroscope as long as the positive object is held in place If the finger is removed and the object taken away, the gold leaf stays deflected The overall charge is now negative
Plenary: Can you explain How can you give a gold leaf electroscope a positive charge? How does a Van der Graaf generator make your hair stand up? What is the cause of lightning?
Solutions Bring a negative charged object close to it. Earth the electroscope by touching it. The electrons will leave the metal plate and rod. Remove the finger and the object. Big rubber bands move over a piece of felt and strip away the felt's electrons. The electrons move up the rubber band to the metal ball and into the person. The electrons repel each other, so they try to get as far away from each other as possible. We see this effect when the volunteer's hair moves as far away from the body as it can! Clouds become charged by friction and the charge separates. The top of the clouds become positively charged and the bottom becomes negatively charged. The cloud's electric field stretches through the space surrounding it. Electrons on Earth's outer surface are repelled.this creates an opposite charge on the Earth's surface. A lightning bolt begins with the development of a step leader. Excess electrons on the bottom of the cloud begin a journey through the conducting air to the ground following a zigzag path.
Key words Conductor electrons flow freely Insulator the flow of electrons does not readily happen Charge the storage of electrical energy Electroscope - an instrument for detecting and measuring electricity Electrostatic - relating to stationary electric charges or fields as opposed to electric currents Ion - an atom or molecule with a net electric charge due to the loss or gain of one or more electron