Charge Current + Energy Power And Resistance

Question 1

Word definition of electric current

Answer 1

rate of flow of charge

Question 2

Word definition of the coulomb

Answer 2

The charge transferred when a current of 1 amp flows for 1 second

Question 3

State Kirchhoff’s first law

Answer 3

-The sum of the currents entering a junction is equal to the sum of the currents leaving the junction.
-This law is a consequence of the conservation of charge.

Question 4

What is electron/mean drift velocity

Answer 4

The average velocity of an electron as it moves along a wire due to a potential difference , colliding with the the positive metal ions

Question 5

Define potential difference

Answer 5

The energy transferred per unit charge when electrical energy is transferred into another form of energy

Question 6

Define e.m.f

Answer 6

The energy transferred per unit charge when another form of energy is transferred into electrical energy

Question 7

State kirchhoff’s second law

Answer 7

In a closed loop, the sum of the e.m.fs is equal to the sum of the potential differences

Question 8

Define resistivity

Answer 8

A property of the material itself defined by the equation:
p=RA/L

Question 9

Define resistance

Answer 9

Potential difference/ current

Question 10

Define power

Answer 10

The rate at which energy is transferred

Question 11

What is meant by the kilowatt hour

Answer 11

The amount of energy transferred when a 1 kW device is operated for 1 hour

Question 12

What are charge carriers

Answer 12

Mobile charged particles capable of transferring charge

Question 13

Describe the charge carriers in metals and electrolytes

Answer 13

• delocalised electrons in a metal
  -ions in a solution

Question 14

What is meant by conventional current

Answer 14

The rate of flow of charge from the positive to to the negative terminal

Question 15

What is meant by electron flow

Answer 15

The rate of flow of charge from the negative terminal to the positive terminal (in the opposite direction to conventional current)

Question 16

What is meant when the charge on a charge carrier is quantised ?

Answer 16

Net charge on a particle is given by
Q = ne ,where n is the number of electrons added or removed and also the quantised charge value for the particle since Q is a multiple of e

Question 17

What is meant by the elementary charge and state it’s magnitude

Answer 17

e - the electric charge carried by single electron
1.6x10^-19 c

Question 18

Describe the difference between conductors, semiconductors and insulators in terms of the number density n

Answer 18

• conductors , large value of n often in the range of 10^28 /m^3
  -semiconductors , n value between insulators and conductors
• insulators , very small value of n , close to 0

Question 19

Define the volt

Answer 19

1volt = 1 joule of energy transferred per coulomb

Question 20

Define the ohm

Answer 20

1 ohm = 1 volt per unit ampere

Question 21

What is ohms law

Answer 21

The current in a wire is directly proportional to the potential difference across it provided that temperature and other physical conditions are constant

Question 22

Describe how the resistance of an LDR varies with light intensity

Answer 22

When incident light intensity increases the resistance of the LDR decreases (vice versa)

Question 23

State the equations for power

Answer 23

P=E/t , P =(I^2)R , P=IV ,P=(v^2)/R

Question 24

State the equations for energy

Answer 24

E=IVt , E=QV

Question 25

Describe how the resistance of a pure metal wire is affected by temperature

Answer 25

Resistance increases linearly with increasing temperature

Question 26

Describe an experiment to investigate the IV characteristics of a component

Answer 26

-Vary the resistance of the variable resistor to change the p.d of the circuit
-measure current with an ammeter
-measure p.d with a voltmeter
-plot a graph of v against I (v y axis and I x axis
-the graph should be a straight line through origin if ohms law is obeyed
-R =v/I

Question 27

Describe an experiment to determine the resistivity of a wire

Answer 27

-measure diameter of wire and take multiple readings along the wire to work out average
-calculate area using A = п(d/2)^2
-vary the length of the wire L
-Measure the current using an ammeter
-measure the p.d using a voltmeter
-Calculate the resistance for each length (using R=v/I)
-Plot a graph of R against L, graph should be straight line through origin
- p =RA/L

Question 28

Why must the current be kept small during the resistivity experiment

Answer 28

-resistivity depends on temperature
-current flowing causes wire temp to increase
- :. temp is not kept constant

Question 29

describe how the resistance of a negative temperature coefficient (NTC) thermistor is affected by changes in temperature.

Answer 29

When the temperature increase , resistance decreases

Question 30

describe how the resistance of a light dependent resistor (LDR) varies with light intensity.

Answer 30

Resistance decreases as light intensity increases