P14: Light

Question 1

properties

convex lens

Answer 1

• focus light inwards (CONVERGING)
• used for magnifying glass/binoculars
• corrects longsightedness - focuses focus on retina

Question 2

properties

concave lenses

Answer 2

• spread light outwards (diverging)
• correct short sightedness , as light is focused in FRONT of retina so spread light out to focus on retina

Question 3

magnification ?

Answer 3

image height/object height

Question 4

which colour has shortest/longest wavelength/frequncy?

Answer 4

RED - Longest wavelength/ lowest frequency
VIOLET - shortest wavelength/ highest frequency

Question 5

specular reflection?

Answer 5

reflection from smooth surface in a single direction (shiny appearance)
( angle of reflection= angle of incidence)

Question 6

diffuse reflection?

Answer 6

reflection from rough surface causes scattering
- when light scatters, leaves surface in all direction (causes matt appearance)

Question 7

how can white light be speperated into all its colours?

Answer 7

• pass it through a prism
• light will refract
• violet refract most (highest frequ) and red refract least
• each colour has different wavelength , so refracts differently creating a spectrum

Question 8

how do colour filters work?

Answer 8

work by absorbing certain wavelengths and transmitting other wavelengths
e.g if white light passes through red filter, red is transmittted , others are absorbed

Question 9

how are colours of opaque object determined?

Answer 9

determined by which wavelengths of light are more strongly reflected
- wavelengths that are not reflected are absorbed - appear BLACK

e.g white light upon green surface will only have green light reflected

Question 10

An object will appear white if ..

Answer 10

all wavelengths are reflected equally

Question 11

an object will appear transparent if ..

Answer 11

all the light is TRANSMITTED, and only small amount is reflected and absorbed

Question 12

difference between transparent object and translucent ?

Answer 12

Transparent objects transmit all light that enters the object , without absorbtion.
Translucent objects let light pass through them, but light is scattered/refracted

Question 13

what is a black body?

Answer 13

an object that absorbs all the radiation it recieves (doesnt transmit/reflect any)
- emits all types of radiation

Question 14

the hotter the body…

Answer 14

• the greater amount of radiation released per second (more powerful)
• the greater amount of high frequency radiation released (x rays)

Question 15

how is a body kept at constant temperature?

Answer 15

the body absorbs radiation at the same rate as emitting it
- initially absorbs more radiation than it emits
- as it gets hotter, it emits more radiation
- soon, it will emit the same it absorbs

Question 16

how to increase/decrease temperature of body?

Answer 16

INCREASES : absorbs more energy that it emitts
DECREASE: energy is released faster than it absorbs

Question 17

how is temperature on Earth kept at a balance?

Answer 17

• earth recieves most thermal enrgy from sun
• at same time, Earth emits its own thermal radiation, with slightly longer wavelength (low frequ - less energy) than the radiation recieved
• greenhouse gases absorb /reflect back longer wavelength IR from earth - preventing it escaping to space

Question 18

what contributes to the greenhouse effect?

Answer 18

the rate of absorbtion/emmission of radiation on Earth

• some radiation is reflected back to space
• some radiation is absorbed by earth or absorbed by greenhouse gases and re- emmitted to earth

Question 19

what is focal length and what factors determine this length?

Answer 19

the distance between the centre of lens to focal point
- material lens is made from
- shape of lens

Question 20

what happens to focal point if lens is more curved?

Answer 20

moves closer to lens
- more curved it is, refracted at a greater angle

Question 21

what is meant by

virtual image?

Answer 21

• cannot be projected onto a screen
• appears behind lens
• only seen from looking through lens

Question 22

what colour is best and worst absorber/emitter of radiation

Answer 22

best : black
worst : shiny