Electrical Quantities
Visão Geral
Rub a balloon on your hair and it sticks to the wall; that tiny transfer of electrons is the same electric charge that, made to flow, powers everything from a torch to a city. Charge, current and the fields around charges are the starting point of all electricity.
In this lesson you will learn about positive and negative charge, how friction charges objects by moving electrons, the difference between conductors and insulators, and how current is the flow of charge. You will use the equation \(Q = It\), describe electric fields and distinguish direct from alternating current.
Objetivos
- State that there are positive and negative charges
- State that positive charges repel other positive charges, negative charges repel other negative charges, but positive charges attract negative charges
- Describe simple experiments to show the production of electrostatic charges by friction and to show the detection of electrostatic charges
- Explain that charging of solids by friction involves only a transfer of negative charge (electrons)
- Describe an experiment to distinguish between electrical conductors and insulators
- Recall and use a simple electron model to explain the difference between electrical conductors and insulators and give typical examples
- Know that electric current is related to the flow of charge
- Describe the use of ammeters (analogue and digital) with different ranges
- Describe electrical conduction in metals in terms of the movement of free electrons
- Know the difference between direct current (d.c.) and alternating current (a.c.)
- [Supplement] State that charge is measured in coulombs
- [Supplement] Describe an electric field as a region in which an electric charge experiences a force
- [Supplement] State that the direction of an electric field at a point is the direction of the force on a positive charge at that point
- [Supplement] Describe simple electric field patterns, including the direction of the field: (a) around a point charge (b) around a charged conducting sphere (c) between two oppositely charged parallel conducting plates (end effects will not be examined)
- [Supplement] Define electric current as the charge passing a point per unit time; recall and use the equation Q I = t
- [Supplement] State that conventional current is from positive to negative and that the flow of free electrons is from negative to positive
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- Two negatively charged objects placed near each other will: A. attract B. repel C. do nothing D. become neutral Answer: B
- When an object is charged negatively by friction, it has: A. gained protons B. gained electrons C. lost electrons D. lost neutrons Answer: B
- A current of 4 A flows for 10 s. The charge that passes is: A. 0.4 C B. 2.5 C C. 40 C D. 14 C Answer: C
- Conventional current is taken to flow: A. from negative to positive B. from positive to negative C. in both directions at once D. only in insulators Answer: B
- Metals conduct electricity because they contain: A. free electrons B. free protons C. no charges D. only positive ions that move Answer: A
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Describe how current is related to charge and time, and distinguish between direct current and alternating current
"Physics: Ohm's law" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/physics/pages/19-1-ohms-law. Access for free at https://openstax.org/books/physics/pages/1-introduction
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