P3.1 - Everything in the Specification

X-rays are part of the [blank_start]electromagnetic[blank_end] spectrum. They have a very [blank_start]short[blank_end] wavelength and cause [blank_start]ionisation[blank_end].

Name the four key properties of X-rays: 1. They affect a [blank_start]photographic film[blank_end] in the same way as [blank_start]light[blank_end]. 2. They are [blank_start]absorbed[blank_end] by [blank_start]metal and bone[blank_end]. 3. They are [blank_start]transmitted[blank_end] by soft [blank_start]tissue[blank_end]. 4. Their [blank_start]wavelength[blank_end] is of the same [blank_start]order of magnitude[blank_end] as the [blank_start]diameter[blank_end] of an atom.

The range of human hearing is from 20-200,000 Hertz.

CCDs ([blank_start]charge[blank_end]-[blank_start]coupled[blank_end] [blank_start]devices[blank_end]) allow [blank_start]X-ray[blank_end] images to be formed [blank_start]electronically[blank_end].

X-rays are ionising, so they can cause genetic mutations which harm cells.

Name three ways in which X-rays can be used in medicine.

Name three ways in which ultrasound can be used in medicine.

X-rays are longitudinal; Ultrasound waves are transverse.

Radiographers take precautions to minimise the [blank_start]radiation[blank_end] [blank_start]dose[blank_end] from X-rays. They do this by wearing lead [blank_start]aprons[blank_end], or standing behind a lead [blank_start]screen[blank_end], or [blank_start]leaving[blank_end] the [blank_start]room[blank_end] while scans are being done. This reduces the [blank_start]exposure[blank_end] time, and provides shielding.

Ultrasound [blank_start]waves[blank_end] are [blank_start]partially reflected[blank_end] when they meet a boundary between two different [blank_start]media[blank_end]. The [blank_start]time taken for[blank_end] the [blank_start]reflections[blank_end] to reach a detector can be used to determine how [blank_start]far away[blank_end] that boundary is.

How are ultrasound waves produced?

Fill in the blanks about the safety and image quality of X-rays and ultrasound. SAFETY: [blank_start]Ultrasound[blank_end] is [blank_start]non-ionising[blank_end] and [blank_start]safe[blank_end]. They [blank_start]can[blank_end] be used on babies. [blank_start]X-rays[blank_end] are [blank_start]ionising[blank_end], and can cause [blank_start]genetic mutations[blank_end] which harm [blank_start]cells[blank_end]. They [blank_start]cannot[blank_end] be used on babies. CT scans use [blank_start]more[blank_end] [blank_start]X-rays[blank_end], so are [blank_start]more[blank_end] ionising. They [blank_start]increase[blank_end] the [blank_start]radiation dose[blank_end] even more. They [blank_start]cannot[blank_end] be used on babies. IMAGE QUALITY: [blank_start]Ultrasound[blank_end] images are usually [blank_start]fuzzy.[blank_end] [blank_start]X-ray[blank_end] images are [blank_start]clear[blank_end] if showing [blank_start]bone or metal[blank_end] - otherwise, they are [blank_start]fuzzy[blank_end]. CT scans are clear, [blank_start]three-dimensional[blank_end] and [blank_start]high-resolution[blank_end]. They can be used to diagnose [blank_start]complicated illnesses[blank_end].

REFRACTION - The [blank_start]change[blank_end] in [blank_start]direction[blank_end] of [blank_start]light[blank_end] as it passes from one [blank_start]medium[blank_end] to another

When refracted into a denser medium, light bends away from the normal.

Explain how refraction occurs at a boundary. 1) The [blank_start]ray of light[blank_end] reaches a boundary between two different [blank_start]media.[blank_end] 2) One side of the [blank_start]ray[blank_end] hits the [blank_start]particles[blank_end] of a different [blank_start]density[blank_end] first. 3) This causes that side to either [blank_start]slow down[blank_end] or [blank_start]speed up[blank_end]. 4) This causes the [blank_start]light ray[blank_end] to turn.

A ray of light that is perpendicular to the normal will not refract.

REFRACTIVE INDEX - The [blank_start]speed[blank_end] at which [blank_start]light[blank_end] [blank_start]travels[blank_end] through a [blank_start]medium[blank_end].

The three facets of the nature of an image are: - It is [blank_start]real[blank_end]/[blank_start]virtual[blank_end]. - It is [blank_start]upright[blank_end]/i[blank_start]nverted[blank_end]. - It is [blank_start]enlarged[blank_end]/d[blank_start]iminished[blank_end].

[blank_start]Total internal reflection[blank_end] occurs when... - The [blank_start]angle of incidence[blank_end] is [blank_start]greater than[blank_end] the [blank_start]critical angle[blank_end]. - Light is moving from a [blank_start]more dense[blank_end] to a [blank_start]less dense[blank_end] [blank_start]medium.[blank_end]

Label the ray diagram.

How is an image formed?

Give one use of a convex lens. A m[blank_start]agnifying[blank_end] g[blank_start]lass[blank_end].

What is the nature of an image produced by a diverging lens? Real or Virtual: [blank_start]Virtual[blank_end] Upright or Inverted: [blank_start]Upright[blank_end] Enlarged or Diminished: [blank_start]Diminished[blank_end]

Fill in the blanks to complete the table showing the natures of images produced by a converging lens.

Fill in the blanks to label the structure of the eye.

Fill in the blanks to complete the function of each of the parts of the human eye. [blank_start]PUPIL[blank_end] - A hole in the eye that lets light in. [blank_start]LENS[blank_end] - A [blank_start]converging[blank_end] [blank_start]lens[blank_end] which focuses light onto the retina. RETINA - A collection of [blank_start]rods[blank_end] and [blank_start]cone[blank_end] cells at the [blank_start]back[blank_end] of the eye which release an [blank_start]electrical[blank_end] [blank_start]impulse[blank_end] when light hits them. OPTIC NERVE - A nerve which carries the electrical impulse to the brain. [blank_start]CORNEA[blank_end] - A screen which protects the eye and does some refraction. IRIS - A muscle which [blank_start]expands[blank_end] if too much light is present, and [blank_start]contracts[blank_end] if not enough light is present. This changes the size of the [blank_start]pupil.[blank_end] [blank_start]CILIARY MUSCLE[blank_end] - A muscle which contracts to make the lens [blank_start]thinner[blank_end], and expands to make the lens [blank_start]thicker[blank_end]. [blank_start]SUSPENSORY LIGAMENT[blank_end] - A ligament that connects [blank_start]ciliary[blank_end] [blank_start]muscles[blank_end] to the [blank_start]lens[blank_end].

If an object is close-by, the lens becomes thicker and lots of refraction occurs.

Drag and drop the correct words to complete the passage. [blank_start]MYOPIA[blank_end] (Short-sightedness): - This defect is caused either by the eyeball being too [blank_start]long[blank_end] or the eye lens being unable to focus. - Too [blank_start]much[blank_end] refraction is occurring, causing light to focus [blank_start]in front of[blank_end] the retina. - To stop this, we place a [blank_start]diverging[blank_end] lens in front of the retina. [blank_start]HYPERMETROPIA[blank_end] (Long-sightedness): - This defect is caused either by the eyeball being too [blank_start]short[blank_end] or the lens being unable to focus. - Too [blank_start]little[blank_end] refraction is occurring, and light focuses [blank_start]behind[blank_end] the retina. - To stop this, we place a [blank_start]converging[blank_end] lens in front of the retina.

The [blank_start]near[blank_end] point is approximately [blank_start]25[blank_end]cm; the [blank_start]far[blank_end] point is [blank_start]infinity[blank_end].

Fill in the blanks to complete the table of similarities between the eye and a camera.

For a given focal [blank_start]length[blank_end], the greater the [blank_start]refractive[blank_end] index, the [blank_start]flatter[blank_end] the lens.

The focal [blank_start]length[blank_end] of a lens is determined by: - The [blank_start]refractive[blank_end] [blank_start]index[blank_end] of the material from which the lens is made - The [blank_start]curvature[blank_end] of the surface of the lens

REFRACTIVE INDEX - The [blank_start]speed[blank_end] at which light [blank_start]travels[blank_end] through a [blank_start]medium[blank_end].

Optical [blank_start]fibres[blank_end] can carry [blank_start]visible[blank_end] [blank_start]light[blank_end] over long distances. They work by [blank_start]bouncing[blank_end] waves off the sides of a [blank_start]thin[blank_end] inner core of [blank_start]glass[blank_end] or plastic. The wave enters at one end and is [blank_start]reflected[blank_end] repeatedly until it emerges at the other end. This is known as [blank_start]total[blank_end] [blank_start]internal[blank_end] [blank_start]reflection[blank_end].

The [blank_start]higher[blank_end] the [blank_start]refractive index[blank_end] of a given material, the [blank_start]lower[blank_end] the [blank_start]critical angle[blank_end] of the material.

ENDOSCOPE - A [blank_start]thin[blank_end] tube containing [blank_start]optical[blank_end] [blank_start]fibres[blank_end] that let surgeons examine inside the body. Endoscopes consist of two bundles of [blank_start]optical[blank_end] [blank_start]fibres[blank_end] - one to carry light, and one to carry an [blank_start]image[blank_end] back. The [blank_start]image[blank_end] can be seen through an eyepiece or as a full-colour [blank_start]image[blank_end]. Endoscopes allow [blank_start]keyhole[blank_end] surgery to take place.

Lasers are narrow, intense beams of light, and they emit light waves of varying wavelengths.

Give the four main ways that lasers can be used. - Lasers can be used in surgery to cut through [blank_start]body tissue[blank_end]. - Lasers [blank_start]cauterise[blank_end] (burn and seal shut) small blood vessels as they cut through the tissue. - Lasers can treat [blank_start]skin[blank_end] conditions such as [blank_start]acne scars.[blank_end] - Lasers are used in [blank_start]laser eye[blank_end] surgery.

What is the role of a laser in laser eye surgery?

CT scans use [blank_start]X-rays[blank_end] to produce high-[blank_start]resolution[blank_end] images of soft and hard [blank_start]tissue[blank_end]. The patient is put inside a [blank_start]cylindrical[blank_end] scanner, and an [blank_start]X-ray[blank_end] beam is fired through the body from an [blank_start]X-ray[blank_end] [blank_start]tube[blank_end] and is picked up by [blank_start]detectors[blank_end] on the other side. The tube and detectors are [blank_start]rotated[blank_end] throughout the scan. A computer interprets the signals from the detectors to produce a [blank_start]two-dimensional[blank_end] image. Many individual CT scans can be combined to create a [blank_start]three-dimensional[blank_end] image.

X-rays can cause [blank_start]ionisation[blank_end] (i.e. they kill living cells), so can be used to treat [blank_start]cancer[blank_end]. The X-rays are focused on a [blank_start]tumour[blank_end] using a [blank_start]wide[blank_end] beam. This beam is rotated around the patient with the [blank_start]tumour[blank_end] at the centre. This minimises the [blank_start]exposure[blank_end] of normal cells to [blank_start]radiation[blank_end], so reduces the chances of the rest of the body being damaged.

Label the three areas with 'AIR' or 'GLASS' depending on what material you think light is being refracted into.

What is the [blank_start]principal focus[blank_end] of a [blank_start]converging[blank_end] lens? - The point where [blank_start]rays[blank_end] hitting the lens [blank_start]parallel[blank_end] to the axis all meet. What is the [blank_start]principal[blank_end] focus of a [blank_start]diverging[blank_end] lens? - The point where [blank_start]rays[blank_end] hitting the lens [blank_start]parallel[blank_end] to the axis all appear to meet.

If the angle of incidence is [blank_start]less than[blank_end] the critical angle, most of the light passes out but some light is internally [blank_start]reflected[blank_end]. If the angle of incidence is [blank_start]equal to[blank_end] the critical angle, the emerging ray comes out along the [blank_start]surface[blank_end] and more internal reflection occurs. If the angle of incidence is [blank_start]greater than[blank_end] the critical angle, no light comes out - it is [blank_start]totally[blank_end] [blank_start]internally[blank_end] reflected.