23-27;Electric charge/Fields/Cathode ray tube/

Question 1

electrical nature of matter

Answer 1

all atoms are made up of protons, neutrons and electrons

classical model of atom = +ively charged nucleus = made up of protons and neutrons and a number of -vely charged e- in orbit

e-= 1 “ quantum “ of -ive charge

proton = 1 quantum of positive charge, but it is of opposite polarity

Electric charge = coulombs

Question 2

behaviour of electric charges

Answer 2

same polarity = repel each other

unlike charges = strong attractive forces

force between charged particles proportional to product of charges, inversely proportional to square of distance between them

Question 3

flow of electric charge

Answer 3

outer e-s of metal atoms are loosely bound and can be easily detached to move through material

Question 4

conductors

Answer 4

metals are good conductors of electricity = availability of free charge carrier metals

Question 5

insulators

Answer 5

EG rubber, ceramics

e-s tightly bound to parent atoms = difficult for e- charges to move through materials

Question 6

semi-conductors

Answer 6

offer intermediate resistance to charge flow

used to manufacture transistors and other solid electronic devices

Question 7

what is electroscope

Answer 7

simple device that illustrates movements of charges

has a metal rod with 2 strips of very thin metal foil attached to bottom, lower end of rod in glass to protect delicate foil strips, rod separated from case by rubber insulator

Question 8

how do electroscopes work

Answer 8

has a net -ive/+ive charge to repel foil strips

+ive rod brought to top
= attracts e- from other part of rod = top of electroscope will be -ively charged

bottom of rod +ively charged due to deficiency in e-s = repulsion of like charges = foil separates

Question 9

electric current

Answer 9

a measure of amount of charge which passes through per sec, 1 C = 1 Amp/1sec

Question 10

electric field strength

Answer 10

force per unit charge exerted upon any point

Question 11

electric field

Answer 11

direction of electric field is the direction of the force on a +ive test charge

around charges can be represented by lines of force, if lines extend outward=+ive point charge, inward=-ive point charge

will drop of rapidly w/ distance from charge

Question 12

what happens if u bring 2 small positive test charges together

Answer 12

would experience repulsive force

Question 13

point charge

Answer 13

conc of change at mathematical point

Question 14

potential

Answer 14

electric potential energy per unit charge

Question 15

capacitance

Answer 15

charge stored per volt of electric potential difference

Question 16

capacitor

Answer 16

set of parallel plates

used to store electric charges in a state of elevated electric potential, the stored charge is released to do work by discharging the capacitor

EG defibrillator = large capacitor

Question 17

how does defibrillator work

Answer 17

several Js of electrical energy stored in defibrillator

when electrodes connected to patient’s body, body forms a conducting discharge path = large current flows for an instant

Question 18

cathode ray tube

Answer 18

device that forms visual display of e- beam from e- gun

Question 19

how does cathode ray tube work

Answer 19

e- gun placed in evacuated glass tube and aimed, high speed e- beam strikes phosphorous coating on one end of tube = gives of light = forms visual image of e- beam = cathode ray

Question 20

why are cathode ray tubes useful

Answer 20

due to the position of phosphorous coating, screen can be moved easily and rapidly = forms moving display of electrical signals = ECG signal

2 deflection plates added to move bean = deflection is proportional to voltage between deflection plates = calibrated for visual measurement of voltage of deflection plate

Question 21

oscilloscope

Answer 21

cathode ray tube w/ associated amplifiers and other electronics

horizontal deflection of e- beam used as time measurement = causing beam to sweep across phosphorous screen at uniform, predetermined speed