Lesson 4 — current, voltage and resistance

• Science
• Middelbare school
• havo
• Leerjaar 2

Class layout – Science

Class layout – Science

Chapter 9 Electricity

This lesson

• Recap
• series and parallel
• Current, voltage & resistance
• Ohms law

Electricity is: a flow of free electrons flowing from a negatively charged pole to a positively charged pole.

This flow of electrons is called: electric current. 

• The symbol for electric current is: I
• The unit of electric current is ampere (A)

1 ampere stands for 1 coulomb flowing by per second (1 coulomb per second).

• 1 coulomb stands for 6.24 x 10¹⁸ electrons
• Example: on average a current of 1,5 A flows through phone charging cable while it is charging. This mean 1,5 coulombs are flowing through that cable per second.

The formula to calculate current is: 

I=​t​​Q​​

current=​time​​charge​​

 Currnet is measured with an ammeter

ammeter

Practice problem

In a school classroom there are approximately 9 LED lamps. At the end of the day after all the lamps have been turned off someone came back, because they forgot something. They turned the lamps on and took 2,5 minutes to find what they were looking for. Through one LED lamp flows a current of 30 mA. Calculate how much electric charge went through these 9 lamps during that time.

In a school classroom there are approximately 9 LED lamps. At the end of the day after all the lamps have been turned off someone came back, because they forgot something. They turned the lamps on and took 2,5 minutes to find what they were looking for. Through one LED lamp flows a current of 30 mA. Calculate how much electric charge went through these 9 lamps during that time.

In a school classroom there are approximately 9 LED lamps. At the end of the day after all the lamps have been turned off someone came back, because they forgot something. They turned the lamps on and took 2,5 minutes to find what they were looking for. Through one LED lamp flows a current of 30 mA. Calculate how much electric charge went through these 9 lamps during that time.

Given:

- 9 LED lamps

- turned on for 2,5 minutes (t = 150s)

- each with a current of 30 mA (I = 0,03 A)

In a school classroom there are approximately 9 LED lamps. At the end of the day after all the lamps have been turned off someone came back, because they forgot something. They turned the lamps on and took 2,5 minutes to find what they were looking for. Through one LED lamp flows a current of 30 mA. Calculate how much electric charge went through these 9 lamps during that time.

Given:

- 9 LED lamps

- turned on for 2,5 minutes (t = 150s)

- each with a current of 30 mA (I = 0,03 A)

Asked: How much electric charge went through these 9 lamps during that time.

In a school classroom there are approximately 9 LED lamps. At the end of the day after all the lamps have been turned off someone came back, because they forgot something. They turned the lamps on and took 2,5 minutes to find what they were looking for. Through one LED lamp flows a current of 30 mA. Calculate how much electric charge went through these 9 lamps during that time.

Given:

- 9 LED lamps

- turned on for 2,5 minutes (t = 150s)

- each with a current of 30 mA (I = 0,03 A)

Asked: How much electric charge went through these 9 lamps during that time.

Formula: 

In a school classroom there are approximately 9 LED lamps. At the end of the day after all the lamps have been turned off someone came back, because they forgot something. They turned the lamps on and took 2,5 minutes to find what they were looking for. Through one LED lamp flows a current of 30 mA. Calculate how much electric charge went through these 9 lamps during that time.

Given:

- 9 LED lamps

- turned on for 2,5 minutes (t = 150s)

- each with a current of 30 mA (I = 0,03 A)

Asked: How much electric charge went through these 9 lamps during that time.

Formula: 

I=​t​​Q​​

In a school classroom there are approximately 9 LED lamps. At the end of the day after all the lamps have been turned off someone came back, because they forgot something. They turned the lamps on and took 2,5 minutes to find what they were looking for. Through one LED lamp flows a current of 30 mA. Calculate how much electric charge went through these 9 lamps during that time.

Given:

- 9 LED lamps

- turned on for 2,5 minutes (t = 150s)

- each with a current of 30 mA (I = 0,03 A)

Asked: How much electric charge went through these 9 lamps during that time.

Formula: 

I=​t​​Q​​

Q=I⋅t

In a school classroom there are approximately 9 LED lamps. At the end of the day after all the lamps have been turned off someone came back, because they forgot something. They turned the lamps on and took 2,5 minutes to find what they were looking for. Through one LED lamp flows a current of 30 mA. Calculate how much electric charge went through these 9 lamps during that time.

Given:

- 9 LED lamps

- turned on for 2,5 minutes (t = 150s)

- each with a current of 30 mA (I = 0,03 A)

Asked: How much electric charge went through these 9 lamps during that time.

Formula: 

Calculation:

I=​t​​Q​​

Q=I⋅t

In a school classroom there are approximately 9 LED lamps. At the end of the day after all the lamps have been turned off someone came back, because they forgot something. They turned the lamps on and took 2,5 minutes to find what they were looking for. Through one LED lamp flows a current of 30 mA. Calculate how much electric charge went through these 9 lamps during that time.

Given:

- 9 LED lamps

- turned on for 2,5 minutes (t = 150s)

- each with a current of 30 mA (I = 0,03 A)

Asked: How much electric charge went through these 9 lamps during that time.

Formula: 

Calculation:

I=​t​​Q​​

Q=I⋅t

Q​1lamp​​=0.03⋅150=4.5C

In a school classroom there are approximately 9 LED lamps. At the end of the day after all the lamps have been turned off someone came back, because they forgot something. They turned the lamps on and took 2,5 minutes to find what they were looking for. Through one LED lamp flows a current of 30 mA. Calculate how much electric charge went through these 9 lamps during that time.

Given:

- 9 LED lamps

- turned on for 2,5 minutes (t = 150s)

- each with a current of 30 mA (I = 0,03 A)

Asked: How much electric charge went through these 9 lamps during that time.

Formula: 

Calculation:

I=​t​​Q​​

Q=I⋅t

Q​1lamp​​=0.03⋅150=4.5C

Q​alllamps​​=4.5C⋅9=40.5C

Series and parallel circuits

Current (I):

• The amount of charge flowing by per second (coulombs/ second).
• Expressed in amperes (A)

Current (I):

• The amount of charge flowing by per second (coulombs/ second).
• Expressed in amperes (A)

Voltage (U):

• The difference in electrical potential energy between two points in a circuit.
• Expressed in volts (V)

Current (I):

• The amount of charge flowing by per second (coulombs/ second).
• Expressed in amperes (A)

Voltage (U):

• The difference in electrical potential energy between two points in a circuit.
• Expressed in volts (V)

Resistance (R):

• The amount something resists the flow of current.
• Expressed in ohms (Ω)

The voltage over a power source gest turned up. The resistance of the circuit connected to it stays the same. The current in the circuit will increase/ stay the same/ decrease.

A resistor gets added to a circuit causing the resistance to increase. the voltage over the circuit stays the same. The current in the circuit will increase/ stay the same/ decrease.

Ohm's law

Current=​Resistance​​Voltage​​

I=​R​​U​​

quantity	unit
Current (I)	Ampere (A)
Voltage (U)	Volt (V)
Resistance (R)	Ohm (Ω)

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?