P4 - Electric Circuits

Question 1

List the 2 types of circuits

Answer 1

Series and Parallel

Question 2

define static charge

Answer 2

electrical charge that is unable to flow

Question 3

what is static charge caused by

Answer 3

friction which leads to electrons being transferred to another body

Question 4

what can generate static electricity

practical

Answer 4

Vandegraff generator

Question 5

Give one use of static electricity

Answer 5

• painting metal (e.g. cars)
• photocopier
• insecticides

Question 6

Give the danger of static electricity

Answer 6

sparks can be caused when a charged object is discharged by being earthed

Question 7

define current

Answer 7

the rate of flow of electrical charge in a circuit

Question 8

equation for current (A)

Answer 8

I = Q / t
Amps = Coulombs / seconds
current = charge / time

Question 9

define electrical charge

Answer 9

a property of matter that causes it to experience a force

Question 10

Does current add up or is it the same across components in a series circuit?

Answer 10

Current is the same across all components in a series circuit.

Question 11

Does current add up or is it the same across components in a parallel circuit?

Answer 11

Current adds up in a parallel circuit.

Question 12

define potential difference

in terms of electrical potential

Answer 12

measure of difference in electric potential energy between 2 points

Question 13

define potential difference

in terms of force

Answer 13

measure of force or “push” P.D. gives the current

P.D. - potential difference

Question 14

equation for potential difference

Answer 14

V = W / Q
Volts = Joules / Coulombs
voltage = energy / charge

Question 15

Does voltage add up or is it the same across components in a series circuit?

Answer 15

Voltage adds up in a series circuit

Question 16

Does voltage add up or is it the same across components in a parallel circuit?

Answer 16

Voltage is the same across all components in a parallel circuit.

Question 17

Why does voltage add up in a series circuit?

Answer 17

Work done by the battery on the charge (coulombs) to “push” it must always equal the work done on all the components, otherwise energy would be lost

work done - energy transferred buckets example

Question 18

define resistance

Answer 18

measure of how difficult it is for electrons to move in an electrical circuit

Question 19

what 4 factors affect resistance, explain why they cause more collisions

Answer 19

• material - density and structure
• thickness - less space
• length - longer
• temperature - more vibrations

Question 20

formula for Ohm’s law

Answer 20

V = IR
V = AΩ
voltage = current * resistance

Question 21

define ohmic conductor

Answer 21

a conductor or component that adheres to Ohm’s law

Question 22

Describe the relationship between current and voltage in a fixed resistor

Answer 22

The current of the fixed resistor (at constant temp) is directly proportional to the voltage across it. Ohmic conductor

x = y

Question 23

Describe the relationship between current and voltage in a filament bulb

Answer 23

The lamp’s resistance increases as temperature increases. The current through lamp increases but starts to plateau as voltage increases, not diretly proportinal. Non-Ohmic conductor

x = y³

Question 24

Describe the relationship between current and voltage in a diode

Answer 24

Current can only flow in one direction because if the voltage would be negative current is 0.

x = log y + c

Question 25

describe how a thermistor works

in terms of temperature

Answer 25

A thermistor has a high resistance when it is cold and a low resistance when it is hot.

like the opposite of a regular condutor in terms of temp

Question 26

describe how a LDR works

in terms of light

Answer 26

An LDR has a high resistance when light intensity is low and a low resistance when light intensity is high

Question 27

The rule for resistance in a series circuit.

Answer 27

Resistance adds up in a series circuit
R_T = R₁ + R₂

Question 28

The rule for resistance in a parallel circuit.

Answer 28

Resistance decreases when adding more parallel connections to a circuit

Question 29

The rule for resistance in a series circuit - WHY does it happen?

Answer 29

The voltage across each resistor is shared.

Question 30

The rule for resistance in a parallel circuit - WHY does it happen?

Answer 30

The total voltage is constant across each resistor, so adding a resistor increases the total current. R = V / I, so if the voltage is constant, increasing the current will result in a lower resistance.