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Year 10
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Resistance of a hot metal

I can explain why the resistance of a metal filament changes as the p.d. across it increases.

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Year 10
OCR
Higher

Resistance of a hot metal

I can explain why the resistance of a metal filament changes as the p.d. across it increases.

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Lesson details

Key learning points

  1. As the p.d. across a filament lamp increases, it gets hotter and current through it increases in a non-ohmic way.
  2. The greater the p.d. across a filament lamp, the greater its resistance.
  3. A metal is made of a lattice of positively charged ions with negatively charged electrons between.
  4. As a current flows through metal, electrons moving through the ion lattice cause it to vibrate more vigorously.
  5. The more vigorously the ions (ion lattice) vibrate, the hotter the metal and the higher its resistance.

Keywords

  • Filament lamp - a type of lamp that uses a hot wire to emit light

  • Ohmic conductor - a conductor for which the current is directly proportional to the p.d.

  • Directly proportional - a relationship between variables in which one is a multiple of the other

  • Metal ion - a metal atom that has lost one or more outer electrons and has become positively charged

  • Free electron - an electron from the outer shell of an atom that is free to move from ion to ion through a metal

Common misconception

The gradient of an I-V graph is equal to 1/R because I = V ÷ R.

Explain how the equation for a straight line graph y = mx + c does not apply in this case because the graph is not a straight line.


To help you plan your year 10 physics lesson on: Resistance of a hot metal, download all teaching resources for free and adapt to suit your pupils' needs...

Encourage pupils to take readings of current and p.d. from their graphs in order to calculate resistance for different brightnesses of the bulb to show that the resistance changes as the bulb gets brighter.
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This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Starter quiz

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6 Questions

Q1.
Which of the following components is represented by the circuit symbol shown?
An image in a quiz
Correct answer: a filament lamp
a light emitting diode
a motor
a laser
Q2.
What happens to the current through a filament lamp as the p.d. across it is increased?
it decreases
Correct answer: it increases
it stays the same
it continuously varies
Q3.
What is the resistance of a filament lamp if it has a current of 0.25 A when a p.d. of 0.5 V is applied across it?
0.125 Ω
0.5 Ω
0.75 Ω
Correct answer: 2.0 Ω
Q4.
Which of the following statements about the I–V graph of a filament lamp is correct?
current is on the x–axis
resistance is on the x–axis
Correct answer: p.d. is on the x–axis
Q5.
If the p.d. across a filament lamp increases at a steady rate, how does the current through it change as the p.d. becomes higher?
Correct answer: it increases less quickly than when the p.d. across it is lower
it increases as the same rate as when the p.d. across it is lower
it increases more quickly than when the p.d. across it is lower
Q6.
What is the resistance of the filament lamp at a p.d. of 3.0 V, according to the I–V graph shown?
An image in a quiz
1.0 Ω
2.0 Ω
Correct answer: 3.0 Ω
4.0 Ω

Exit quiz

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6 Questions

Q1.
Which of the following components does the I–V graph shown represent?
An image in a quiz
a resistor
a diode
Correct answer: a filament lamp
a thermistor
Q2.
Which of the following is an ohmic conductor?
Correct answer: a resistor
a filament lamp
an electric heater
Q3.
Which of the following statements about ohmic conductors and non–ohmic conductors is correct?
an I–V graph for ohmic conductors is a curved line
an I–V graph for non–ohmic conductors is a straight line
Correct answer: an I–V graph for ohmic conductors is a straight line through the origin
the resistance of non–ohmic conductors is constant
Q4.
In the model of a metal shown, what do the blue circles represent?
An image in a quiz
Correct answer: electrons
positrons
neutrons
protons
Q5.
In the model of a metal shown, what do the black circles represent?
An image in a quiz
atoms
electrons
negatively charged ions
Correct answer: positively charged ions
Q6.
What happens to the electrons and metal ions when a metal is heated?
The electrons move as before and the metal ions vibrate more vigorously.
The electrons move more quickly and the metal ions vibrate less vigorously.
The electrons move more quickly and the metal ions vibrate as before.
Correct answer: The electrons move more quickly and the metal ions vibrate more vigorously.