Two lamps light the same zinc plate, one dim and one bright. Second after second, each lamp's light lands on the plate and delivers energy to it. The bright lamp delivers more.
In the waves topic, you saw that a wave carries energy from place to place. Light is no exception: a lit surface is a surface receiving energy. This lesson names the quantity that measures how strongly a light delivers.
Light shining on a surface delivers energy to the surface.
The delivery goes on second after second, for as long as the light shines.
One lamp might deliver 18 J to a plate each second; a brighter lamp might deliver 30 J each second to the same plate.
Intensity is what your eye reads as brightness: the higher a light's intensity, the brighter it looks.
A dimmer lamp delivers less energy each second, and a lamp that is switched off delivers none.
Intensity says nothing about the light's frequency.
A dim ultraviolet lamp has low intensity at high frequency; a bright red lamp has high intensity at low frequency.
A flashlight delivers 6 J of light energy to a wall each second. A floodlight delivers 45 J to the same wall each second. Which light has the higher intensity?
Intensity is the energy a light delivers to a surface each second.
The flashlight delivers 6 J each second; the floodlight delivers 45 J each second.
45 J each second is more than 6 J each second.
The floodlight's light has the higher intensity, and it looks brighter on the wall.
Xiomara dims a lamp that lights a metal plate. What happens to the energy the plate receives each second?
Dimming a lamp lowers the light's intensity.
Intensity is the energy delivered to the plate each second.
Lower intensity means less energy delivered each second.
The plate receives less energy each second.
A desk lamp delivers 18 J of light energy each second to a zinc plate. A floodlight delivers 30 J each second to the same plate. Which light has the higher intensity?
Zelda says: 'Of two lamps lighting the same plate, the one that delivers more energy to the plate each second has the higher intensity.' Is Zelda correct?
Una says: 'A light's intensity is the total energy the lamp has delivered since it was switched on.' Is Una correct?
Which quantity is a light's intensity?
Two lamps light one wall. Vasco can see that the patch lit by the second lamp is brighter than the patch lit by the first. What does that tell him about the two lights?
The energy a light delivers to a surface each second has a name. What is it called?