E01-04 - Current, Potential difference and Resistance

Question 1

What is current in terms of charge carriers

Answer 1

-current is the flow of electrons inside a material

Question 2

What does the current measure

Answer 2

-the rate of flow of charge

Question 3

What is defined as the amp

Answer 3

-charge flowing through a wire per second

Question 4

What is the formula relating current, charge and time

Answer 4

Q=It

Question 5

What is conventional current

Answer 5

-Current flowing from positive to negative - the opposite way to how electrons travel

Question 6

What is needed for an Ammeter to measure amps

Answer 6

• in series

- low resistance - with a lower resistance more current can flow and get measured.

Question 7

How is charge quantified

Answer 7

-Quantified by Q.

Question 8

What is the actual charge of an electron/proton

Answer 8

• +/- 1.6x10^-19

Question 9

What is the definition of charge

Answer 9

-A coulomb of charge is the current past a point in one second

Question 10

How is energy transferred in a circuit

Answer 10

• Energy starts at the cell as CHEMICAL energy
• Energy transferred to the charge carriers as they pass the cell - ELECTRICAL energy
• They then move around the circuit and release it at the component to OTHER FORMS of energy
• The circuit then repeats

Question 11

What is EMF

Answer 11

• amount of chemical energy transferred to electrical energy
• measured in Volts [V]
• Has the ε symbol

Question 12

What is potential difference

Answer 12

• Amount of energy per unit of charge transferred from electrical to other forms
• V=IR

Question 13

How do you use a voltmetre to measure potential difference

Answer 13

• parrel to component
• Needs high resistance so that there is a low current through the voltmetre so there is a more accurate proportion of current through the component

Question 14

What is defined as the volt

Answer 14

-the potential difference between two points when work is done to move the charge

Question 15

What is the equation linking potential difference, work done and charge

Answer 15

• V=W/Q

Question 16

How is energy gained by particles with potential difference

Answer 16

• when a charged particle moves away from the oppositely charged plate work is done to the particle (W=QV)
• Once the particle is released, all work is transferred to kinetic energy(QV=1/2mV^2
• This accelerates the particle once it is released as opposite charges attract

Question 17

What is resistance

Answer 17

• the ratio of PD across the component to the current through the component
• R=V/I
• Ohm

Question 18

What causes resistance

Answer 18

-When charge carriers moving through a conductor collide with the conductor, slowing the current down.

Question 19

What is ohm’s law

Answer 19

-For an OHMIC conductor, at a constant temperature, the current is directly proportional to the potential difference

Question 20

What materials are ohmic conductors

Answer 20

-almost all metals

Question 21

What is a conductor

Answer 21

-Where there are a large number of free charge carriers relative to the material

Question 22

What is an insulator

Answer 22

-Where there are no or very few charge carriers relative to the material

Question 23

What is a semi-conductor

Answer 23

• Where the number of charge carriers increases when an external force is applied to the semi-conductive material
• More charge carriers are released with more force.

Question 24

What are two examples of a semiconductor

Answer 24

• Thermistor

- LDR

Question 25

How does a thermistor work

Answer 25

-When heated, more charge carriers are released, I increases, R decreases

Question 26

How does an LDR work

Answer 26

-allows charge carriers to release when light is shone at it, I increases, R decreases