【4th Grade Science】How Electric Current Works: Let's Learn About Electrical Paths!
Hello everyone! Let’s have some fun learning about "how electric current works" in science.
When you power a toy car or turn on a flashlight, there are "dry cell batteries" inside, right? Actually, just by changing the way you connect the batteries, you can change how fast a motor spins or how bright a light bulb glows.
If you feel like "science is a bit tough," don't worry! We'll go through it one step at a time, using familiar examples!
1. Direction of Current and Motors
First, the flow of electricity is called electric current. There is a fixed "direction" in which current flows.
The Rule of Current Direction
Current flows from the positive (+) terminal of a dry cell battery toward the negative (-) terminal.
What happens if you reverse this flow?
How Motors Spin
When you connect a dry cell battery to a motor with a propeller, if you reverse the orientation of the battery, the direction the motor spins also reverses.
Example: If the propeller was spinning clockwise, it will spin counter-clockwise if you reverse the battery.
Key Points:
・Current flows from "plus (+)" to "minus (-)"!
・If the direction of the current changes, the direction of the motor's spin changes too!
2. How to Connect Dry Cell Batteries (Using 2 Batteries)
When using two dry cell batteries, there are two types of connections. This is the most important part of this unit!
① Series Connection
This is the method of connecting two batteries in a straight line (a single path). Imagine connecting the plus of one battery to the minus of the other.
【Characteristics】
・The current becomes stronger!
・The motor spins very fast.
・The light bulb glows very brightly.
② Parallel Connection
This is the method of connecting two batteries by placing them side-by-side (so the path splits in two). You connect the plus terminals together and the minus terminals together.
【Characteristics】
・The strength of the current is the same as with just one battery.
・The speed of the motor and the brightness of the light bulb are the same as with one battery.
・However, the batteries last longer!
Fun Fact: Remember with an analogy!
A series connection is like two people standing in a line to push a heavy load with all their might. You have double the power, but you get tired quickly.
A parallel connection is like two people standing side-by-side, taking turns (or splitting the effort) to carry a load. You have the power of one person, but you can keep going for a long time!
Summary:
・If you want a power boost, use series connection.
・If you want things to last longer, use parallel connection.
3. Measuring Current with a "Galvanometer"
You can't see electricity, but by using a tool called a galvanometer, you can see exactly how much current is flowing.
Tips for Using a Galvanometer
1. Check that the needle is pointing to "0".
2. In a series connection, the needle swings significantly (the current is large).
3. In a parallel connection, the swing of the needle is about the same as with one battery.
4. If the direction of the current is reversed, the direction the needle swings also reverses.
Common Mistake:
Be careful not to forget to put the galvanometer in the circuit, which would lead to a "short circuit" where the positive and negative terminals are connected directly. The batteries will get hot and that’s dangerous!
4. How Photovoltaic Cells Work
Have you seen "solar panels" on house roofs or calculators lately? In science, we call them photovoltaic cells.
Secrets of Photovoltaic Cells
・Photovoltaic cells create electricity when they are exposed to light (such as sunlight).
・The stronger the light hitting the cell, the larger the current that flows.
・If you use a mirror to collect more light, the motor will spin even faster.
・Conversely, on cloudy or rainy days, or if you create a shadow with your hand, the current becomes smaller.
Key Point:
Unlike dry cell batteries, photovoltaic cells do not have electricity "stored" inside. They are like "tiny power plants" that only produce electricity when there is light.
5. Finally: Important Checkpoints
I’ve summarized the points that are easy to get wrong on tests or in class. If you remember these, you'll be perfect!
Q1: How can you make a motor spin faster?
A1: Connect the dry cell batteries in a series connection. Or, increase the light hitting the photovoltaic cell.
Q2: If you connect two dry cell batteries in a parallel connection, what happens to the light bulb?
A2: The brightness remains the same as with one battery. (This is the trickiest one!)
Q3: How do you determine the direction of the current?
A3: Use a galvanometer or observe the direction in which the motor spins.
At first, the words "series" and "parallel" might feel a bit difficult, but if you draw the diagrams many times, you will remember them naturally. It's okay—take your time and work at your own pace!