Combined decks Flashcards
What changes could be made to a convex lense to produce an enlarged and upright image?
- Move the lens closer to the object so that it lies within the focal length of the lens to produce a virtual, enlarged and upright image.
- Use a thinner/less curved lens with a larger radius of curvature, so that the object lies within the focal length.
- Decrease the refractive index of the glass so its focal length increases, so that the object lies within the focal length.
Distance of an object away from a concave mirror
- Distance will be negative, as image formed is virtual
- The image has been magnified 3x, so the image distance is 3x the object distance from the mirror
- Therefore, di = -3do
- Substitute values into 1/f = 1/do + 1/di
Difference between images produced in concave/convex mirrors (between f and c)
- The image formed by the convex mirror is upright, diminished and virtual.
- Convex mirrors are diverging mirrors, which means that no real light rays intersect on the same side of the mirror as the light source. This means all images in a convex mirror are virtual. All virtual images are upright and diminished.
- The image formed by the convex mirror is diminished because virtual light rays travel less before they appear to meet.
- The image formed by the concave mirror is inverted, enlarged and real.
- Concave mirrors are converging mirrors, which means that real light rays will intersect (if the object is beyond the focal point) on the same side of the mirror as the light source.
- The image formed by the concave mirror is enlarged because real reflected light rays travel longer before they meet.
- The largest image will be produced when the object is as close to f as possible. At this position, the reflected rays are nearly parallel, causing a large di and hi.
Distinguishing between real and virtual images
- A real image occurs where light rays converge, whereas a virtual image occurs where light rays only appear to converge.
- A virtual image is upright, and cannot be projected onto a screen.
- A real image is inverted, and can be projected onto a screen.
Light shining through two slits and producing a pattern of multiple slits.
- Bright bands are due to constructive interference, which are regions where the crest of one wave combines with the crest of another. The path
difference is either zero (central band) or a whole
number of wavelengths. - Dark bands are due to destructive interference,
which are regions where the crest of one wave combines with the
trough of another wave. The path difference is
either half a wavelength or an odd mulitiple of half
wavelengths.
Sound heard walking past two speakers
The person walking in a straight line closer to the speakers will hear the loud and soft sounds at shorter distances as compared to the person walking in a straight line further away. This is because the antinodal lines fan out from the speakers, and therefore the further away one is from the speakers, the further apart the loud and soft sounds heard will be.
- Louder sound is heard where waves from two sources constructively interfere. This is because the path difference between the two sound waves is nλ, so the total amplitude of the resultant wave increases, creating a louder sound.
- Quieter sound is heard where waves from two sources deconstructively interfere. This is because the path difference between the two sound waves is 1/2λ, so the total amplitude of the resultant wave decreases, creating a quieter sound.
Find if point x is a node or antinode
- Calculate the frequency (f = 1/T)
- Calculate the wavelength (v = fλ)
- Calculate the path difference (distance to point x from 1 opening - distance to point x from other opening)
- Path difference / wavelength
- If the result is half a wavelength, point x must be a node. If the result is a whole wavelength, point x must be an antinode.
Images formed by concave lenses
Regardless of the position of the object, the image will always be virtual, upright and diminished. The image is located on the object’s side of the lens.
Images formed by convex lenses
(Same as images formed in concave mirrors)
- The object is beyond C
An inverted, real and diminished image will be formed. - The object is at C
An inverted, real image will be formed, that is the same size as the object. - The object is between C & F
An inverted, real and enlarged image will be formed. - The object is at F
No image will be formed. - The object is in front of F
An upright, virtual and enlarged image will be formed, that is located on the object’s side of the lens.
Images formed in concave mirrors
- The object is beyond C
An inverted, real and diminished image will be formed. - The object is at C
An inverted, real image will be formed, that is the same size as the object. - The object is between C & F
An inverted, real and enlarged image will be formed. - The object is at F
No image will be formed. - The object is in front of F
An upright, virtual and enlarged image will be formed, that is behind the mirror (eg. dentist mirror).
Images formed in convex mirrors
Regardless of the position of the object, the image will always be virtual, upright and diminished. The image is located behind the mirror.
Equation for critical angle
sinθc = n2 sin90°/n1
Where,
- θc is the critical angle
- n2 is the absolute refractive indices for medium 2
- n1 is the absolute refractive indices for medium 1
Total internal reflection
For total internal reflection to occur, the angle of incidence has to be greater than the critical angle, and the light ray must be travelling from a medium of a higher refractive index (optical density) to one of a lower refractive index.
Therefore, when rays of light at a very large angle of incidence hit the cold/hot air interface, the angle of incidence in greater than the critical angle, which causes all the light rays to undergo total internal reflection.
Critical angle
The critical angle is the angle of incidence (θ1), when the angle of refraction is 90°.
Refractive index
If two different mediums (water/air/glass) have different refractive indices, light will refract differently at the boundary between them.
When refraction occurs…
The frequency of the wave does not change when crossing the boundary. From v = fλ, velocity is directly proportional to wavelength. Therefore, as the frequency remains constant, and the wave velocity increases, the wavelength will increase also.
Refraction
- Refraction is the change in the speed of a light wave as it travels from one medium into another, causing it to change direction.
- When light travels into a medium of greater density, it refracts towards the normal as the medium of higher density has a higher refractive index.
- When light travels into a medium of less density, it defracts away from the normal as the medium of less density has a lower refractive index.
- Rays of light from (the bottom of the pool) are refracted (bent) before reaching a persons eye. Our brain makes us think that the rays are coming straight backwards from where they are, making the object appear closer to the surface of the water than it actually is.
Equation for path difference
with nodal lines
PS1 - PS2 = (n - 1/2) λ
Where,
- PS1 is the number of lines between source 1 and the point
- PS2 is the number of lines between source 2 and the point
- n is the nodal line number
- λ is the wavelength
Note - Nodal line number is taken from the central dotted line
Equation for path difference
with anti-nodal lines
PS1 - PS2 = nλ
Where,
- PS1 is the number of lines between source 1 and the point
- PS2 is the number of lines between source 2 and the point
- n is the antinodal line number
- λ is the wavelength
Note - Antinodal line number is taken after the central dotted line (middle line = 0)
Diffraction
- Diffraction is the process of waves spreading as they pass through a gap
- Maximum diffraction occurs when the wavelength of the wave is approximately equal to the size of the gap.
- The wavelength of a wave does not change when it is diffracted.
eg. Sound waves have a longer wavelength compared to light waves. Because of this longer wavelength, the soundwaves are more able to diffract around barriers (as the openings are around the same order of size as the wavelength of the sound waves). Comparatively, lightwaves cannot diffract as much around barriers. Therefore, often people can hear objects, but not see them.
Reflection and transmission of a pulse
Heavy string to light string
Heavy string to light string
- Pulse moves slower along heavy string and faster along the light string.
- A small pulse reflected and the same way up as the original pulse moves back along the heavy string.
- The amplitude will be smaller when reflected due to a decrease in energy (as not all the energy is reflected).
Reflection and transmission of a pulse
Light string to heavy string
Light string to heavy string
- Pulse moves slower along heavy string and faster along the light string.
- A small pulse reflected and upside down to the original pulse moves back along the light string.
- The amplitude will be smaller when reflected due to a decrease in energy (as not all the energy is reflected).
- As the pulses in the light string are travelling faster, they are further from the boundary when reflected.
Effect of adding an ammeter in parallel
- Adding an ammeter in parallel will short circuit the connected bulb, as all the current will go through the ammeter instead due to the low resistance of the ammeter (0V across connected bulb). This will cause the connected bulb to go out, and result in the total resistance of the circuit decreasing.
- This will cause the overall current in the circuit to increase (I = V/R)
- Therefore, the voltage of any bulbs connected in series will increase (V = IR) and the voltage of any bulbs connected in parallel will decrease (Voltage is directly proportional to resistance (V = IR), therefore when the current is the same, as resistance decreases, voltage decreases also).
- Therefore, the power used by any bulbs connected in series will have more power, and any bulbs connected in parallel will have less power (P = IV).