• Pixel-art sticker of Warmohm, personifying Temperature Coefficient of Resistance, with the caption “Heat My Wire, I Resist More.”

IndexForces & FieldsSticker

Warmohm

Temperature Coefficient of Resistance Physics

\[R = R_0 (1 + \alpha \Delta T)\]
$4.99 USD
$4.99 USD
Sale Sold out

Meet Warmohm, a coil of wire who resists current more as he heats up. Hotter atoms vibrate harder and scatter electrons more. Copper rises about 0.0039 per kelvin, so warming by 100 K adds about 39 percent. A glowing tungsten filament exceeds ten times its cold resistance. Pixel-art kiss-cut sticker in 2, 3, 4 and 6 inches; equation, symbols and sources in the physics panel below.

Size
Surface

Flat $6 shipping worldwideMade to order, ships in 2–5 business days

Details

Size3″ × 3″

3″ × 3″ kiss-cut sticker.

Shipping

Flat $6 shipping on every order, worldwide, whatever's in it.

Delivery times & where we ship

Returns & replacements21 days

Every item is printed to order, so we can’t accept returns or exchanges for change of mind, or if you ordered the wrong size or colour.

Print defect, misprint, damage or the wrong item? We’ll send a free replacement, or a refund if you prefer. Report it within 21 days of delivery with a photo; no need to send it back.

Full refund & replacement policy

The physics

Meet Warmohm, a coil of wire who resists current more and more as he heats up.

In a metal, current is carried by free electrons. As the metal gets hotter, its atoms vibrate harder and the electrons bump into them more often. So the resistance rises with temperature.

Over a moderate range the rise is close to a straight line, R = R₀(1 + αΔT), where α is the temperature coefficient. For copper α ≈ 0.0039 per kelvin. Warming a copper wire by 100 K raises its resistance by about 39 percent.

A tungsten lamp filament is far more extreme. It runs near 2800 K and its resistance when glowing is more than ten times its value when cold. That is why old bulbs usually blew at the moment they were switched on, when a big surge of current rushed in.

Platinum resistance thermometers use this effect to measure temperature with great accuracy. Semiconductors go the other way, with a resistance that falls as they heat, and they are used as thermistors.

Equations

\[R = R_0 (1 + \alpha \Delta T)\]
SymbolMeaningUnit
\(R\) resistance \(\mathrm{Ω}\)
\(R_0\) resistance at reference temperature \(\mathrm{Ω}\)
\(\alpha\) temperature coefficient \(\mathrm{1/K}\)
\(\Delta T\) temperature change \(\mathrm{K}\)

Sources

  1. OpenStax University Physics Vol. 2 — Resistivity and Resistance
  2. Wikipedia — Temperature coefficient

Field notes

View all
  • Pixel-art illustration for this Pixelated Physics post: a pixel pendulum bob character swinging over a circular floor marked with pixel pegs, a few pegs knocked over showing the swing plane slowly turning, a pixel Earth spinning in the window

    How Does a Foucault Pendulum Prove Earth Rotates?

    A long pendulum’s swing plane slowly turns relative to the floor. Foucault showed in 1851 that the turn is Earth’s rotation made visible. The rate is 360° times the sine...

    How Does a Foucault Pendulum Prove Earth Rotates?

    A long pendulum’s swing plane slowly turns relative to the floor. Foucault showed in 1851 that the turn is Earth’s rotation made visible. The rate is 360° times the sine...

  • Pixel-art Einstein ring: a foreground galaxy bends the light of a galaxy directly behind it into a circular ring of arcs centered on it

    How Does Gravity Bend Light? Einstein Rings and...

    Gravity bends light because spacetime is curved. The 1919 eclipse measured the Sun’s deflection; Einstein’s 1936 note foresaw stellar lenses; modern telescopes image Einstein rings. Here is the physics without...

    How Does Gravity Bend Light? Einstein Rings and...

    Gravity bends light because spacetime is curved. The 1919 eclipse measured the Sun’s deflection; Einstein’s 1936 note foresaw stellar lenses; modern telescopes image Einstein rings. Here is the physics without...

  • Pixel-art illustration for this Pixelated Physics post: three abstract pixel mascots of early quantum ideas: a glowing light-packet character, a tiny atom with stepped orbit rings, and a fuzzy uncertainty cloud, climbing a staircase of energy levels

    Who Started Quantum Mechanics? Planck, Bohr and...

    Quantum theory did not begin with one paper. Planck quantized energy in 1900, Bohr quantized the atom in 1913, and Heisenberg’s 1925 matrix mechanics plus the 1927 uncertainty relation made...

    Who Started Quantum Mechanics? Planck, Bohr and...

    Quantum theory did not begin with one paper. Planck quantized energy in 1900, Bohr quantized the atom in 1913, and Heisenberg’s 1925 matrix mechanics plus the 1927 uncertainty relation made...

1 3
View all