Electronics
Medical use of radiation
Radiation therapy targets cancer cells, shrinking tumors and preventing their spread.
Radiation sterilization ensures safety by eliminating harmful microbes in medical equipment.
X-rays help diagnose broken bones and detect internal injuries swiftly and accurately by penetrating through skin but not bones allowing the doctor to see through the patient's body without surgery.
Radiotherapy halts cancer growth by damaging DNA within malignant cells.
Resistors control current flow, crucial for limiting current and dividing voltage in circuits.
Thermistors alter resistance with temperature change, (As temperature increases, resistance decreases allowing current to pass through. key in temperature-sensing circuits and thermostats.
The transformer alters voltage in AC circuits, vital for stepping up/down voltage in power distribution.
Advantages of parallel circuits:
The advantages of this kind of circuit are:
The components can be individually controlled, using their own switches
If one component stops working the others will continue to function
A potential divider splits the potential difference of a power source between two components
A step-up transformer has more coils on its secondary coil than its primary coil.
Step-up transformers increase voltage and decrease current
Potential divider equation: V[out]=(R2/(R1+R3))*V[in]
Electrical hazards
Common hazards include:
Damaged Insulation – If someone touches an exposed piece of wire, they could be subjected to a lethal shock
Overheating of cables – Passing too much current through too small a wire can lead to the wire overheating. This could cause a fire or melt the insulations, exposing live wires
Damp conditions – If moisture comes into contact with live wires, the moisture could conduct electricity either causing a short circuit within a device (which could cause a fire) or posing an electrocution risk
Reflection, Refraction
Reflection
Refraction
An incident ray has an arrow pointing towards the boundary
A reflected ray has an arrow pointing away from the boundary
An incident ray has an arrow pointing towards the boundary
A refracted ray has an arrow pointing away from the boundary
Refraction occurs when light passes a boundary between two different transparent media
The only properties that change during refraction are speed and wavelength – the frequency of waves does not change
When light enters a denser medium (such as glass) it slows down and bends towards the normal
Law of reflection: Angle of incidence (i) = Angle of reflection (r)
Snell's law:
n=sin i/sin r
Total Internal Reflection
Total internal reflection (TIR) occurs when:
The angle of incidence is greater than the critical angle and the incident material is denser than the second material
Used in:
Optical fibres e.g. endoscopes
Prisms e.g. periscopes
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The larger the refractive index of a material, the smaller the critical angle
Light rays inside a material with a high refractive index are more likely to be totally internally reflected
n = 1/sin C
The line at right angles (90°) to the boundary is known as the normal
Lens diagrams
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Key terms:
The principal axis is defined as: A line which passes through the centre of a lens
The principal focus, or focal point, is defined as: The point at which rays of light travelling parallel to the principal axis intersect the principal axis and converge or the point at which diverging rays appear to proceed
Focal length is defined as: The distance between the centre of the lens and the principal focus
Converging lenses can be used to correct long-sighted vision
Diverging lenses can be used to correct short-sighted vision