TJC 2023 IP4 Static Electricity Notes

TJC IP4 PHYSICS 2023 IP4 TOPIC 11 – Static Electricity 1 of 11 TOPIC 11 – STATIC ELECTRICITY Content: • Laws of electrostatics • Principles of electrostatics • Electric field • Applications of electrostatics Learning Outcomes: Candidates should be able to: (a) state that there are positive and negative charges and that charge is measured in coulombs (b) state that unlike charges attract and like charges repel (c) describe an electric field as a region in which an electric charge experiences a force (d) draw the electric field of an isolated point charge and recall that the direction of the field lines gives the direction of the force acting on a positive test charge (e) draw the electric field pattern between two isolated point charges (f) show understanding that electrostatic charging by rubbing involves a transfer of electrons (g) describe experiments to show electrostatic charging by induction (h) describe examples where electrostatic charging may be a potential hazard (i) describe the use of electrostatic charging in a photocopier, and apply the use of electrostatic charging to new situations Essential Questions: By the end of the lesson, students should be able to answer the questions: 1. What are the different types of charges existing? 2. What are the interactions between charges? 3. How can you charge an object? 4. How can you distinguish between the types of charges? 5. What are the possible hazards of charges?

TJC IP4 PHYSICS 2023 IP4 TOPIC 11 – Static Electricity 2 of 11 TRIGGER: http://www.express.co.uk/news/uk/265646/The-girl-13-who-could-die-if-she-combs-her-hair Megan Stewart, 13, has a rare condition, Hair Brushing Syndrome, which means she must avoid wearing polyester or touching balloons. Any contact with electrical charges could confuse her brain into switching itself off or sending signals to her heart and lungs to make them do so. Megan has to dampen her hair to reduce static and lie down before combing it and is banned from taking part in school science experiments. The teenager, from Wishaw, Lanarkshire, was diagnosed three years ago, after she collapsed as her mother ¬Sharon brushed her hair. Mrs Stewart, 41, said: “I was brushing her hair when she flopped over and her lips turned blue. I thought she was having a fit, so we called the paramedics. It was really scary.” Megan was taken to Wishaw General Hospital where medics revived her. Neurologists made the diagnosis two months later. Doctors at the Royal Hospital for Sick Children at Yorkhill in Glasgow, believe birth complications may be responsible for the condition. Megan was born three months prematurely, weighing just 2lb 5oz wit h a diaphragmatic hernia, a hole in her stomach leading right up into her chest, which only allowed space for only one lung to grow. She spent the first 18 months of her life in hospital. She also suffers from asthma and dorsal stream dysfunction, a problem with the connection between her eye and brain which means she can’t see fast-moving objects. But the Uddingston Grammar School pupil is determined to get on with her life. She said: “I know not to brush my hair too fast and if I feel unwell to stop doi ng it. I think I know what my limits are. I don’t let it affect me and I can still live a normal life.” How much do you know about static charges? What is an advice you could give a person diagnosed with such a condition? 1 Electrostatic Charge: The study of electric charges which are not moving. LO (a) 1.1 Atomic Structure: 1.2 Two types of electrostatic charges: (a) Positive charges. Consist of: - Protons - Positive ions: formed by atoms losing electrons (b) Negative charges. Consist of: - Electrons - Negative ions: formed by atoms gaining electrons S.I. Unit: coulomb (C) A proton has a positive charge of 1.6 x 10 -19 C. An electron has a negative charge of 1.6 x 10 -19 C. What is the charge carried by 1 electron? Charge carried by 1 electron = - 1.6 x 10-19 C. How many electrons in 1 C of charge? No. of electrons = 1/ 1.6 x 10 -19 C = 6.25 x 1018

TJC IP4 PHYSICS 2023 IP4 TOPIC 11 – Static Electricity 3 of 11 2 Attraction and Repulsion LO (b) The law of electrostatics states that like charges repel and unlike charges attract. The force of attraction and repulsion increases as the distance between charges decreases. Only repulsion between a specimen and a charged object is a sure test that allows us to conclude that the specimen is charged (not neutral). The specimen should have a similar charge as the charged object. Example 1: A small ball with zero net charge is positively charged on one side, and equally negatively charged on the other side. The ball is placed near a positive point charge (charge with a very small volume) as shown. positive point charge negatively charged positively charged a. State and explain whether the ball would be attracted toward, repelled from, or unaffected by the positive point charge. The ball will be attracted towards the point charge as the attractive force between point charge and negative hemisphere is larger than the repulsive force between point charge and positive hemisphere. This is due to the negative hemisphere being closer to the point charge. b. State the factors that affect the strength of the forces between the two objects. The amount of charge in both objects; The distance between the centres of the two objects.

TJC IP4 PHYSICS 2023 IP4 TOPIC 11 – Static Electricity 4 of 11 Electrical Conductors allow electric charges to flow through them easily. Eg: metals, acids, graphite, water, salt solutions and ionized air. Metals are good electric conductors due to the presence of free electrons which can move freely when there is an electric force. Electrical Insulators do not allow electric charges to flow through them easily. The electrons are tightly bound to their own atoms and not free to move between atoms. Eg: rubber, glass and plastic. Main difference between conductors and insulators Conductors have ‘free electrons’ (found in metals and graphite) or free moving ions (water, weak acids and salt solutions) that are able to move freely. Insulators do not have such ‘free electrons’ or free moving ions. Question 1: Can positive charges move in a metallic conductor? * Note: Always refer to the movement of negative charges (which are electrons) and not positive charges. 3 Electric Field LO (c), (d) & (e) 3.1 Definition: An electric field is a region where an electric charge experiences an electric force. ▪ This electric field can be illustrated by drawing electric lines of force. An electric line of force is the path a positive charge would take if it was free to move ▪ That is, the direction of electric field is the direction of how a positive test charge would move. ▪ A stronger electric field is denoted by having more electric lines of force which are drawn closer to each other. 3.2 Drawing Electric Lines of Force (Non-uniform electric fields): ▪ draw arrows to indicate correct direction of electric field [Check how a positive test charge would move to identify the direction of electric field lines (lines must begin from positive charges and end on negative charges)] ▪ No field lines can cross or touch each other ▪ Appropriate spacings/gaps between electric field lines [small spacings → strong field] ▪ Field pattern is symmetrical (for O-level or IP questions)

TJC IP4 PHYSICS 2023 IP4 TOPIC 11 – Static Electricity 5 of 11 Electric field around a positively charged sphere. Electric field around a negatively charged sphere. Combined electric field between two opposite charges Combined electric field between two similar positive charges