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Difference between revisions of "Electrical Resistance"
Line 4: Line 4:
  
 
===About Resistance===
 
===About Resistance===
−
: The [[SI Unit|unit]] of '''resistance''' is the [[Ohm]] ([[Ω]]).
+
: The [[SI Unit|unit]] of '''resistance''' is the [[Ohm]] (Ω).
 
: '''Resistance''' cannot be directly [[measure]]d. '''Resistance''' must be calculated by dividing the [[Potential Difference]] by the [[Electrical Current|Current]].
 
: '''Resistance''' cannot be directly [[measure]]d. '''Resistance''' must be calculated by dividing the [[Potential Difference]] by the [[Electrical Current|Current]].
 
: [[Electrical Conductor|Conductors]] have a low '''resistance''' and [[Electrical Insulator|insulator]]s have a high '''resistance'''.
 
: [[Electrical Conductor|Conductors]] have a low '''resistance''' and [[Electrical Insulator|insulator]]s have a high '''resistance'''.
  
 
===Equation===
 
===Equation===
−
:<math>Resistance = \frac{Potential Difference}{Current}</math>
+
'''Resistance''' = (Potential Difference)/(Current)
 +
 
 
:<math>R = \frac{V}{I}</math>
 
:<math>R = \frac{V}{I}</math>
 
Where:
 
Where:
−
: R = Resistance
+
: <math>R</math> = '''Resistance''' of a [[Electrical Component|component]].
−
: V = Potential Difference
+
: <math>V</math> = The [[Potential Difference]] across the [[Electrical Component|component]].
−
: I = Current
+
: <math>I</math> = The [[Electrical Current|current]] through the [[Electrical Component|component]].
  
 
===Example Calculations===
 
===Example Calculations===
 
{| class="wikitable"
 
{| class="wikitable"
 
|-
 
|-
−
| style="height:20px; width:200px; text-align:center;" |'''A student [[measure]]s a [[Potential Difference|potential difference]] of 5[[V]] across a [[component]] and a [[Electrical Current|current]] of 0.1[[A]]. Calculate the resistance.'''
+
| style="height:20px; width:200px; text-align:center;" |'''A student [[measure]]s a [[Potential Difference|potential difference]] of 5V across a [[component]] and a [[Electrical Current|current]] of 0.1A. Calculate the resistance.'''
−
| style="height:20px; width:200px; text-align:center;" |'''A [[Electrical Bulb|bulb]] has a [[Electrical Current|current]] of 200[[mA]] passing through it and a [[Potential Difference|potential difference]] of 12[[V]] across it. Calculate the resistance of the [[Electrical Bulb|bulb]].'''
+
| style="height:20px; width:200px; text-align:center;" |'''A [[Electrical Bulb|bulb]] has a [[Electrical Current|current]] of 200mA passing through it and a [[Potential Difference|potential difference]] of 12V across it. Calculate the resistance of the [[Electrical Bulb|bulb]].'''
−
| style="height:20px; width:200px; text-align:center;" |'''Calculate the resistance of a [[buzzer]] connected in [[Series Circuit|series]] to a 6[[V]] [[battery]] with an [[ammeter]] reading of 10[[mA]].'''
+
| style="height:20px; width:200px; text-align:center;" |'''Calculate the resistance of a [[buzzer]] connected in [[Series Circuit|series]] to a 6V [[battery]] with an [[ammeter]] reading of 10mA.'''
 
|-
 
|-
 
| style="height:20px; width:200px; text-align:left;" |
 
| style="height:20px; width:200px; text-align:left;" |
−
Potential Difference = 5[[V]]
+
Potential Difference = 5V
  
−
Current = 0.1[[A]]
+
Current = 0.1A
  
 
<math>R = \frac{V}{I}</math>
 
<math>R = \frac{V}{I}</math>
Line 34: Line 35:
 
<math> R = 50 \Omega</math>
 
<math> R = 50 \Omega</math>
 
| style="height:20px; width:200px; text-align:left;" |
 
| style="height:20px; width:200px; text-align:left;" |
−
Potential Difference = 12[[V]]
+
Potential Difference = 12V
  
−
Current = 200[[mA]] = 0.2[[A]]
+
Current = 200[[mA]] = 0.2A
  
 
<math>R = \frac{V}{I}</math>
 
<math>R = \frac{V}{I}</math>
Line 44: Line 45:
 
<math> R = 60 \Omega</math>
 
<math> R = 60 \Omega</math>
 
| style="height:20px; width:200px; text-align:left;" |
 
| style="height:20px; width:200px; text-align:left;" |
−
Potential Difference = 6[[V]]
+
Potential Difference = 6V
  
−
Current = 10[[mA]] = 0.01[[A]]
+
Current = 10mA = 0.01A
  
 
<math>R = \frac{V}{I}</math>
 
<math>R = \frac{V}{I}</math>
Line 53: Line 54:
  
 
<math> R = 600 \Omega</math>
 
<math> R = 600 \Omega</math>
 +
|}
 +
 +
==Key Stage 4==
 +
===Meaning===
 +
'''Resistance''' is the [[ratio]] of [[Potential Difference|potential difference]] to [[Electrical Current|current]].
 +
 +
===About Resistance===
 +
: The [[SI Unit|unit]] of '''resistance''' is the [[Ohm]] ([[Ω]]).
 +
: '''Resistance''' cannot be directly [[measure]]d. '''Resistance''' must be calculated by dividing the [[Potential Difference]] by the [[Electrical Current|Current]].
 +
: [[Electrical Conductor|Conductors]] have a low '''resistance''' and [[Electrical Insulator|insulator]]s have a high '''resistance'''.
 +
 +
===Equation===
 +
'''Resistance''' = (Potential Difference)/(Current)
 +
 +
:<math>R = \frac{V}{I}</math>
 +
Where:
 +
: <math>R</math> = '''Resistance''' of a [[Electrical Component|component]].
 +
: <math>V</math> = The [[Potential Difference]] across the [[Electrical Component|component]].
 +
: <math>I</math> = The [[Electrical Current|current]] through the [[Electrical Component|component]].
 +
 +
===Example Calculations===
 +
{| class="wikitable"
 +
|-
 +
| style="height:20px; width:300px; text-align:center;" |'''A student [[measure]]s a [[Potential Difference|potential difference]] of 5.9[[V]] across a [[component]] and a [[Electrical Current|current]] of 0.11[[A]]. Calculate the resistance correct to two [[Significant Figures|significant figures]].'''
 +
| style="height:20px; width:300px; text-align:center;" |'''Calculate the resistance of a [[buzzer]] connected in [[Series Circuit|series]] to a 9V [[battery]] with an [[ammeter]] reading of 23mA correct to two [[Significant Figures|significant figures]].'''
 +
|-
 +
| style="height:20px; width:200px; text-align:left;" |'''1. State the known quantities in correct [[unit]]s.'''
 +
 +
Potential Difference = 5.9V
 +
 +
Current = 0.11A
 +
 +
 +
| style="height:20px; width:200px; text-align:left;" |'''1. State the known quantities in correct [[unit]]s.'''
 +
 +
Potential Difference = 9V
 +
 +
Current = 23mA = 23x10<sup>-3</sup>A
 +
 +
 +
| style="height:20px; width:200px; text-align:left;" |'''2. [[Substitute (Maths)|Substitute]] the numbers into the [[equation]] and [[Solve (Maths)|solve]].'''
 +
 +
<math>R = \frac{V}{I}</math>
 +
 +
<math>R = \frac{5.9}{0.11}</math>
 +
 +
<math> R = 53.635 \Omega</math>
 +
 +
<math> R \approx 54\Omega</math>
 +
 +
| style="height:20px; width:200px; text-align:left;" |'''2. [[Substitute (Maths)|Substitute]] the numbers into the [[equation]] and [[Solve (Maths)|solve]].'''
 +
 +
<math>R = \frac{V}{I}</math>
 +
 +
<math>R = \frac{9}{23\times10^{-3}}</math>
 +
 +
<math> R = 391.304 \Omega</math>
 +
 +
<math> R \approx 390 \Omega</math>
 
|}
 
|}

Revision as of 15:12, 25 February 2019

Key Stage 3

Meaning

Resistance is a description of how difficult it is to increase the current through a conductor when increasing the potential difference.

About Resistance

The unit of resistance is the Ohm (Ω).
Resistance cannot be directly measured. Resistance must be calculated by dividing the Potential Difference by the Current.
Conductors have a low resistance and insulators have a high resistance.

Equation

Resistance = (Potential Difference)/(Current)

\[R = \frac{V}{I}\] Where: \[R\] = Resistance of a component. \[V\] = The Potential Difference across the component. \[I\] = The current through the component.

Example Calculations

A student measures a potential difference of 5V across a component and a current of 0.1A. Calculate the resistance. A bulb has a current of 200mA passing through it and a potential difference of 12V across it. Calculate the resistance of the bulb. Calculate the resistance of a buzzer connected in series to a 6V battery with an ammeter reading of 10mA.

Potential Difference = 5V

Current = 0.1A

\(R = \frac{V}{I}\)

\(R = \frac{5}{0.1}\)

\( R = 50 \Omega\)

Potential Difference = 12V

Current = 200mA = 0.2A

\(R = \frac{V}{I}\)

\(R = \frac{12}{0.2}\)

\( R = 60 \Omega\)

Potential Difference = 6V

Current = 10mA = 0.01A

\(R = \frac{V}{I}\)

\(R = \frac{6}{0.01}\)

\( R = 600 \Omega\)

Key Stage 4

Meaning

Resistance is the ratio of potential difference to current.

About Resistance

The unit of resistance is the Ohm (Ω).
Resistance cannot be directly measured. Resistance must be calculated by dividing the Potential Difference by the Current.
Conductors have a low resistance and insulators have a high resistance.

Equation

Resistance = (Potential Difference)/(Current)

\[R = \frac{V}{I}\] Where: \[R\] = Resistance of a component. \[V\] = The Potential Difference across the component. \[I\] = The current through the component.

Example Calculations

A student measures a potential difference of 5.9V across a component and a current of 0.11A. Calculate the resistance correct to two significant figures. Calculate the resistance of a buzzer connected in series to a 9V battery with an ammeter reading of 23mA correct to two significant figures.
1. State the known quantities in correct units.

Potential Difference = 5.9V

Current = 0.11A


1. State the known quantities in correct units.

Potential Difference = 9V

Current = 23mA = 23x10-3A


2. Substitute the numbers into the equation and solve.

\(R = \frac{V}{I}\)

\(R = \frac{5.9}{0.11}\)

\( R = 53.635 \Omega\)

\( R \approx 54\Omega\)

2. Substitute the numbers into the equation and solve.

\(R = \frac{V}{I}\)

\(R = \frac{9}{23\times10^{-3}}\)

\( R = 391.304 \Omega\)

\( R \approx 390 \Omega\)

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