Cells in series | Electric current | Physics | Khan Academy

Summary

This video explains the behavior of batteries when connected in series and parallel configurations. In a series connection, batteries combine their voltages, increasing the total voltage, while in parallel, they provide more current. The video focuses on the series setup, explaining how battery emf (electromotive force) adds up and how internal resistances combine as well. It also touches on the impact of reversing battery connections, leading to reduced or negative emf. The concept of internal resistance is briefly covered, emphasizing how it affects overall efficiency.

Takeaways

• 🔋 Batteries can be connected in two ways: series and parallel.
• 🔗 In series connections, batteries are connected end to end, resulting in more voltage.
• 🔋 In parallel connections, batteries are connected across each other, providing more current.
• ⚡ The effective voltage in a series connection is the sum of the individual battery voltages.
• 🔋 EMF (Electromotive Force) represents how much energy the battery provides per coulomb of charge.
• 🔋 In a series, if a charge moves through two batteries with EMFs of 5V and 7V, the total energy transfer is 12 joules, making the effective EMF 12V.
• 🔄 Connecting batteries in reverse (positive to positive or negative to negative) results in a negative voltage, as energy is lost.
• ⚡ Internal resistance of batteries adds up in series, affecting the efficiency and energy loss through heat.
• 🚫 Internal resistance is independent of battery orientation, always summing up regardless of the connection.
• 🔋 Series connections are best when higher voltage is needed, but internal resistance will also increase.

Q & A

What are the two types of battery connections mentioned in the video?

The two types of battery connections mentioned are series connection and parallel connection.

What happens to the voltage when batteries are connected in series?

When batteries are connected in series, their voltages add up, resulting in more voltage.

What happens to the current when batteries are connected in parallel?

In a parallel connection, the batteries provide more current.

What is the meaning of electromotive force (EMF) in the context of batteries?

EMF represents the energy a battery delivers to each coulomb of charge, with the unit being joules per coulomb.

How do you calculate the total EMF when two batteries are connected in series?

The total EMF in a series connection is the sum of the individual EMFs of the batteries. For example, if one battery has an EMF of 5V and another 7V, the total EMF is 12V.

What happens if the batteries are connected with their positive terminals together instead of in the correct series configuration?

If the batteries are connected with their positive terminals together, the total EMF could become negative, depending on the battery values. One battery might subtract its EMF from the other.

What is the role of internal resistance in a battery?

Internal resistance represents the resistance within the battery that causes some of the energy to be lost as heat when a charge moves through the battery.

How does internal resistance behave when batteries are connected in series?

When batteries are connected in series, their internal resistances add up, just like their EMFs do.

Does internal resistance depend on the orientation of the battery connection?

No, internal resistance does not depend on how the batteries are connected. It always adds up in series, regardless of orientation.

When should batteries be connected in series?

Batteries should be connected in series when you need more voltage for a device or circuit.