Lesson 7 — 5.3 Series and parallel

• Physics
• Middelbare school
• vwo
• Leerjaar 3

This lesson

• Recap questions
  
• Resistance, voltage & current — Parallel and series
• Working on exercises.

A electrician is working on a series circuit with a current of 0,83 A flowing through it and a total resistance of 8 Ω. He adds two resistors of 4 Ω each to this circuit. After this he doubles the voltage over the circuit.

What will happen to the current flowing through the circuit after this?

1. You can't tell because you aren't given the voltage over the circuit.
2. It wil double.
3. It will be half as much
4. It will be the same.

 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?

 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

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?

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.

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.

Resistance, voltage & current 

Series and parallel

Equivalent resistance

Resistance, voltage & current — Series circuit

Resistors in series

Voltage in series

Current in series

R​tot​​=R​1​​+R​2​​+R​3​​+...

U​tot​​=U1+U2+U3...

I​tot​​=I​1​​=I​2​​=I​3​​=...

Resistance, voltage & current — Parallel circuit

Resistors in series

Voltage in series

Current in series

​R​​1​​​tot​​=​R​​1​​​1​​+​R​​1​​​2​​+​R​​1​​​3​​+...

I​tot​​=I​1​​+I​2​​+I​3​​=...

U​tot​​=U​1​​=U​2​​=U​3​​=...

Homework

Exercise:

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