Physics MCQ question

Audi SG

Question extracted from TYS

X and Y are lamps with filaments made from the same material. The filament of lamp X is thicker and shorter than that of lamp Y.

When connected to the mains and switched on, which is the brighter lamp and which lamp has the larger resistance?

Brighter lamp larger resistance

X X

X Y

Y X

Y Y

For me, my answer is X is the brighter lamp while Y is the one with larger resistance. Reason being we know that X has lower resistance, so it will have larger current flow , hence brighter.

For the answer given, it is lamp Y for both factors. I suppose they think that Y has a higher resistance, hence higher voltage -> brighter.

What should the better answer be? I did consult my teacher regarding such questions before and she said always relate brightness to current flowing across the component.

Herzog_Zwei SG

Answer is both Y.

The greater the resistance of the filament, the more energy is converted. The filament is now the resistive load.

Heat energy converted exceeds the normal methods of heat removal, ie radiation, convection and conduction.

The electron quatum rings of the filament elements take in the energy and thus has the energy to leap into the ring. But the new elemental structure is thus unstable and has to release the energy to regain stability. The photon will be formed by the excess energy. Accumulation of many photons result in visible light.