unit 8 - electricity

Question 1

like charges ______

unlike charges _______

Answer 1

repel

attract

Question 2

what may happen to the electrons when two objects are rubbed again each other

Answer 2

maybe transferred from one to the other

Question 3

structure of conductors

Answer 3

their electrons are loosely held to their atoms that they can pass freely between them. Those free electrons carry heat and charges

Question 4

structure of insulators

Answer 4

their electrons are tightly held to atoms and not free to move. but can pass by rubbing

Question 5

what is a semiconductor

Answer 5

poor conductor when cold but become a better conductor when the temperature is hot

Question 6

what is the SI unit for charge

Answer 6

coulomb

Question 7

feature of electric field lines

Answer 7

positive to the negative charge

Question 8

what is current

Answer 8

a flow of charge

Question 9

what is the SI unit for current

Answer 9

Ampere

Question 10

what is used to measure armpere

Answer 10

ammeter

Question 11

the current is the same/different at all points in a simple circuit

Answer 11

same

Question 12

formula for charge

Answer 12

charge= current*time

Question 13

what is conventional current

Answer 13

the positive charge is flowing from positive to negative

Question 14

what is SI unit for potential difference

Answer 14

voltage

Question 15

what is the electromotive force

Answer 15

the maximum potential difference of the cell

Question 16

the sum of the p.d.s across the component is equal to the p.d. across the battery, is the statement true

Answer 16

yes

Question 17

how is the voltmeter connect

Answer 17

parallel to the device to measure its voltage

Question 18

si unit for resistance

Answer 18

ohm

Question 19

what is a resistance

Answer 19

a measure of the difficulty of making an electric current from through a component in a circuit

Question 20

formula for resistance

Answer 20

voltage = current* resistance 
V= IR

Question 21

what is voltage

Answer 21

the energy that pushes electrons throughout the circuit

Question 22

factors that increase resistance

Answer 22

more length - directly proportional

less cross-sectional area - less charge will flow at the same time

material - like nichrome

temperature- in metal resistance increases as temperature increases,but in semiconductors resistance decreases.

Question 23

what is the function of resistor and its symbol

Answer 23

increases resistance, keep the p.d. and current at the level that component need

symbol: a rectangle with lines at left and right

Question 24

variable resistor function and its symbol

Answer 24

used for varying current

rectangle and an arrow from bottom left and top right across the rectangle

Question 25

thermistor feature and its symbol

Answer 25

high resistance when cold. low resistance when hot. to detect temperature change

a symbol like a resistor but has a line going through from bottom left to top right and a line at the bottom

Question 26

light-dependent resistor feature and its symbol

Answer 26

high resistance in the dark but low resistance in the light.

a symbol like resistor and has two arrows pointing towards the top surface of the rectangle

Question 27

diodes feature and its symbol

Answer 27

extremely high resistance in one direction but low resistance in the other, so that current will only flow in one direction

a straight horizontal line and the line perpendicular to that and the triangle in the line like the stop button(music or video)

Question 28

what is the ohms law

Answer 28

the current is proportional to the p.d.

Question 29

the formula for proportionality of resistance

Answer 29

(resistance1 * area 1 / length 1) = ( resistance 2 * area 2 / length 2)

Question 30

describe lamps connected in series

Answer 30

share the voltage so each glow dimly

if one lamp is removed, the other goes out as well because the circuit is broken

Question 31

describe lamps connected in parallel

Answer 31

each lamps gets full voltage from the battery

if one is removed the other keep working because it is still part of the unbroken circuit

Question 32

describe current and p.d. in the series circuit

Answer 32

current in each of the components is the same

the total p.d. across all the components is the sum of the p.d.s across each of them

Question 33

describe current and p.d. in the parallel circuit

Answer 33

p.d. across each of the components is the same

the total current in the main circuit is the sum of the currents in the branches

Question 34

formula for resistance in the series circuit

Answer 34

R= R1 + R2

Question 35

formula for resistance in the parallel circuit

Answer 35

1/R = 1/R1 + 1/R2

Question 36

si unit for power

Answer 36

watt (W)

Question 37

formula for power

Answer 37

power = energy transformed/ time taken

Question 38

the formula of power using current

Answer 38

VI= P

Question 39

the formula for energy transformed

Answer 39

E= VIt ( can be QV as well)

Question 40

the main current is alternating/direct current

Answer 40

alternating

Question 41

what is a live wire

Answer 41

where the current comes in

Question 42

what is the neutral wire

Answer 42

where the current ends

Question 43

what is a fuse

Answer 43

it breaks the circuit if the current is too high

Question 44

what is an earth wire

Answer 44

safety wire earths the object so it is safe to touch

Question 45

hazard of electricity

Answer 45

long extension leads
water in sockets
cutting wires