Electrostatics

Question 1

Electric force

Answer 1

• like kinds repel and unlike kinds attract - when two+ atoms join to form a molecule, the molecule contains balanced positives and negatives

Question 2

Electric charges

Answer 2

1. Positive 2. Negative 3. Neutrons

Question 3

Atom facts

Answer 3

• every atom is composed of a positively charged nucleus surrounded by negatively charged electrons - electrons of all atoms are identical - atoms usually have as many electrons as protons, so the atom has zero net charge

Question 4

Conservation of charge

Answer 4

When we charge something, no electrons are created or destroyed, they are just transferred from one material to another - charge is conserved

Question 5

Coulomb’s law

Answer 5

The electrical force decreases inversely as the square of the distance between charged bodies F = k (Q1Q2/d^2) K = 9 x 10^9 N x m^2 /C^2 Electrical forces may be either attractive or repulsive, whereas gravitational forces are only attractive

Question 6

Conductors

Answer 6

(Good conductors) materials where the electron in the outer shell of the atoms is not anchored to the nuclei of particular atoms but is free to wander in the material - metal

Question 7

Insulators

Answer 7

(Poor conductors) materials where the electrons are tightly bound and belong to particular atoms - rubber, glass

Question 8

Semiconductors

Answer 8

Material that can be made to behave sometimes as an insulator and sometimes as a conductor

Question 9

Transistors

Answer 9

Made of thin layers of semiconducting materials sandwiched together - they are used to control the flow of currents in circuits, detect and amplify radio signals, and to produce oscillations in transmitters - they require little power

Question 10

Super conductors

Answer 10

Materials that acquire zero resistance (infinite conductivity) to the flow of charge - occurs at suffice Nelly low or high temperatures

Question 11

Charging by friction

Answer 11

Electrons transferred by friction when materials rub against each other

Question 12

Charging by contact

Answer 12

Negatively charged object contacts a neutral object and electrons move to the neutral object

Question 13

Charging by induction

Answer 13

Redistribution of electric charges by the electrical influence of a charge object close by but not in contact - lightning rod

Question 14

Electrically polarized

Answer 14

When charges of an atom or molecule are aligned so that one side has a slight excess of positive charge and the other side a slight excess of negative charge

Question 15

Electric field

Answer 15

The space around every electrically charged body - contains: magnitude (force per unit charge at any point) and distance (E = F / q) E = electric field at that point F = force at some point in space Q = charge of the body

Question 16

Electric field facts

Answer 16

• direction of the field is defined to be the direction on which a mall positive test charge at rest would be pushed - the electric field is a storehouse of energy - electric fields can be shielded by various materials

Question 17

Electric shield wants

Answer 17

If we want to shield an electric field, whatever is needing to be shielded is surrounded with a conducting surface. When this surface is placed in an electric field, the free chargers in the conducting surface will arrange themselves on the surface of the conductor so that all field contributions inside cancel one another

Question 18

Electric potential

Answer 18

Work is required to push a changed particle against the electric field of a charged body - this will change the electric potential of the particle - electric potential does not equal potential energy - a high electric potential (voltage) means a lot of energy only if a lot of charge is involved - electric potential (aka voltage) = potential energy per unit charge Electrical potential = electic potential energy / charge

Question 19

Electric charge unit

Answer 19

Volt 1 volt = 1 joule of energy per 1 coulomb of charge

Question 20

Answer 20