IB Physics Topic B.5.5 Electric Cells and Variable Resistors Revision Notes (SL/HL)

IB Physics Topic B.5.5 Electric Cells and Variable Resistors Revision Notes (SL/HL) | RevisionDojo

Internal Resistance and Variable Resistors

When you connect a battery to a circuit, you might expect it to deliver its full electromotive force (emf) to the external components.

Definition

Electromotive force

The electromotive force (emf) is the work done per unit charge to move a charge completely around a circuit, including through the battery.

However, this is rarely the case.
Inside every battery, there is internal resistance, an inherent resistance within the cell.

Note

The emf is the maximum potential difference the battery can provide when no current is flowing.

What is Internal Resistance?

Definition

Internal resistance

Internal resistance is the resistance within the battery itself, caused by the materials and chemical reactions inside it.

Hint

This resistance reduces the energy available to the external circuit.

How Does Internal Resistance Affect a Circuit?

When a current $I$ flows through a battery with emf $\varepsilon$ and internal resistance $r$, the potential difference across the battery’s terminals (the terminal voltage) is less than the emf.
This is because some energy is lost as heat within the battery.
The relationship is given by $V = \varepsilon - Ir$, where:
1. $V$ is the terminal voltage.
2. $I$ is the current flowing through the circuit.
3. $r$ is the internal resistance.

Example

If a battery has an emf of 12 V and an internal resistance of 0.5 Ω, and it supplies a current of 2 A to a circuit, the terminal voltage is: $$V = 12 \, \text{V} - (2 \, \text{A} \times 0.5 \, \Omega) = 11 \, \text{V}$$
This means 1 V is lost inside the battery due to its internal resistance.

Calculating Internal Resistance

The total resistance in a circuit with a battery is the sum of the internal resistance $r$ and the external resistance $R$.

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Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

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Note

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Internal Resistance and Variable Resistors

When you connect a battery to a circuit, you might expect it to deliver its full electromotive force (emf) to the external components.

Definition

Electromotive force

The electromotive force (emf) is the work done per unit charge to move a charge completely around a circuit, including through the battery.

However, this is rarely the case.
Inside every battery, there is internal resistance, an inherent resistance within the cell.

Note

The emf is the maximum potential difference the battery can provide when no current is flowing.

What is Internal Resistance?

Definition

Internal resistance

Internal resistance is the resistance within the battery itself, caused by the materials and chemical reactions inside it.

Hint

This resistance reduces the energy available to the external circuit.

How Does Internal Resistance Affect a Circuit?

When a current $I$ flows through a battery with emf $\varepsilon$ and internal resistance $r$, the potential difference across the battery’s terminals (the terminal voltage) is less than the emf.
This is because some energy is lost as heat within the battery.
The relationship is given by $V = \varepsilon - Ir$, where:
1. $V$ is the terminal voltage.
2. $I$ is the current flowing through the circuit.
3. $r$ is the internal resistance.

Example

If a battery has an emf of 12 V and an internal resistance of 0.5 Ω, and it supplies a current of 2 A to a circuit, the terminal voltage is: $$V = 12 \, \text{V} - (2 \, \text{A} \times 0.5 \, \Omega) = 11 \, \text{V}$$
This means 1 V is lost inside the battery due to its internal resistance.

Calculating Internal Resistance

The total resistance in a circuit with a battery is the sum of the internal resistance $r$ and the external resistance $R$.

Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

Topic A - Space, time and motion5 subtopics

Topic B - The particulate nature of matter5 subtopics

Topic C - Wave behaviour5 subtopics

Topic D - Fields4 subtopics

Topic E - Nuclear and quantum physics5 subtopics

IB Physics B.5.5 Electric Cells and Variable Resistors Notes

Topic A - Space, time and motion5 subtopics

Topic B - The particulate nature of matter5 subtopics

Topic C - Wave behaviour5 subtopics

Topic D - Fields4 subtopics

Topic E - Nuclear and quantum physics5 subtopics

Internal Resistance and Variable Resistors

What is Internal Resistance?

How Does Internal Resistance Affect a Circuit?

Calculating Internal Resistance

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Internal Resistance and Variable Resistors

What is Internal Resistance?

How Does Internal Resistance Affect a Circuit?

Calculating Internal Resistance

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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