Lesson 5 — 5,3 Series and paralel

This lesson
  • Quick recap
  • Discussing the homework
  • Different types of Resistors
  • Start 5,3

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This lesson
  • Quick recap
  • Discussing the homework
  • Different types of Resistors
  • Start 5,3

Slide 1 - Tekstslide

Quick recap

Slide 2 - Tekstslide

Current, voltage, Resistance

Water tank comparison.


Slide 3 - Tekstslide

Current, voltage, Resistance

Ohm's law
R=IU
I=RU

Slide 4 - Tekstslide

Specific resistivity
R=Aρl
Every material has a specific measure of how much it resists the flow of current. 

This property is called the
Specific resistivity of a material.

The formula on the right shows what the resistance of a piece of wire becomes.
  • R: Resistance  — Ohm (Ω)
  • ρ: the resistivity — Ohm-meter (Ωm)
  • l: the length of the wire — meters (m)
  • A: the area of the cross section of the wire — (m2)

Slide 5 - Tekstslide

Discussing the homework
Worksheet:
< Part 2 Exercise 1 to 4 + 6 & 7
> Part 2 Exercise 1, 2, 5, 8 & 9

Slide 6 - Tekstslide

Worksheet part 1
Water tank comparison
Unit in terms of water
Property of an electric circuit
Unit
Base units behind this unit
The height difference between the valve and the top of the water.

Joule/ Litre 
Voltage
Volt (v)
Joule/ Coulomb
The flow of water.

Litre/ second
Current
Ampere (A)
Coulomb / second
How open or closed the valve is.
Not required
Resistance
Ohm (Ω)
Not required

Slide 7 - Tekstslide

1) Think about the water tank comparison.
a) The water flow of water will increase / decrease when the valve gets opened more.

b) The electric current in a circuit will increase / decrease when the resistance increases.

c) The flow of water will increase / decrease when the height difference between the valve and the top of the water tank increases.

d) The electric current in a circuit will increase / decrease when the voltage over the circuit increases.

Slide 8 - Tekstslide

2) Which of the circuits below is correct for measuring voltage and current? 

Slide 9 - Tekstslide

 A physicist wants to make a charge of 6,4∙10^-15 C flow through a wire. He knows the resistance of the wire is 25 Ω. He applies a voltage of 8 V over the wire. How long does a current have to flow through the wire to let the required amount of charge flow through it?
Given:
- Required amount of charge: 6,4 • 10^15
- R = 25 Ω
- U = 8 V

Asked:
How long does current have to flow through the write to reach the required amount of charge?

Working:
R = U/I                   I = U/R
Q = I • t                  t = Q/ I

I = 8/ 25 = 0.32 A
t = (6,4 • 10^15)/ 0,32 = 2 • 10^16 seconds

Slide 10 - Tekstslide

 A wire has a cross-section with an area with a radius of 3 cm. The length of this wire is 20 cm. The resistance of this wire is 1,56∙10^(-6) Ω. The temperature of the wire is 20 ºC. What material is it made of? Use the table one 1 on page 79 of Book B to find the answer.
Given:
- r cross section wire = 3 cm = 0,03 m
- A cross section wire = π • r= π  • 0,032 = 0.00282743338 m2
- l wire = 20 cm = 0,2 m.
- R = 1,56 x 10-6 Ω

Asked:
What material is the wire made off? 

Working:
R = (ρ • l) / A                  ρ = (R • A) / l
ρ = ( (1,56 x 10-6) • 0.00282743338) / 0,2 = 0,022 • 10-6 Ωm
This corresponds with the specific resistivity of gold. So the wire must be made of gold.

Slide 11 - Tekstslide

Different types of resistors
  • What is an ohmic resistor?
  •  What material can be used to make an ohmic resistor?
  • Why do other materials not follow Ohms law?
  • What does NTC stand for?
  • What is the relationship between temperature and resistance in an NTC?
  • What would the opposite of an NTC be called?
  • What doe LDR stand for?
  • What is the relationship between light and resistance in an LDR?

Slide 12 - Tekstslide

Different types of resistors
What is an ohmic resistor?
  • A resistor where the resistance is the same regardless of the voltage.

 What material can be used to make an ohmic resistor?
  • Constantan

Why do other materials not follow Ohms law?
  • An increase in voltage causes an increase in current in a circuit. This increases the temperature of the wire. This causes the resistance to increase.

Slide 13 - Tekstslide

Different types of resistors
What does NTC stand for?
  • Negative temperature coefficient. 

What is the relationship between temperature and resistance in an NTC?
  • An increase in temperature causes a decrease in resistance and vice versa.

What would the opposite of an NTC be called?
  • A PTC — Positive Temperature Coefficient.

What doe LDR stand for?
  • Light dependent resistor.

What is the relationship between light and resistance in an LDR?
  • If more light falls on the reistor its resistance will decrease and vice versa.

Slide 14 - Tekstslide

Resistance, voltage & current — Series circuit
Resistors in series


Voltage in series


Current in series


Rtot=R1+R2+R3+...
Utot=U1+U2+U3...
Itot=I1=I2=I3=...

Slide 15 - Tekstslide

Resistance, voltage & current — Parallel circuit
Resistors in series


Voltage in series


Current in series


R1tot=R11+R12+R13+...
Itot=I1+I2+I3=...
Utot=U1=U2=U3=...

Slide 16 - Tekstslide

Homework next lesson
5,3 Exercise 1, 2, 3 & 4

Slide 17 - Tekstslide