Topic 5 - Light and the electromagnetic spectrum

• What is reflection in terms of light?

  Reflection is where light waves encounter a surface and bounce back into the same medium. The angle of incidence = the angle of reflection.

  
• What is refraction in terms of light?

  Refraction is the bending of light when it passes from one medium to another. It occurs due to a change in the speed of light in different substances as they have different densities.
• What is total internal reflection?

  Total internal reflection is the complete reflection of light at the boundary between two different media, occurring when the angle of incidence is greater than the critical angle.

  
• What is the difference between specular and diffuse reflection?

  Specular reflection is when light reflects off a smooth surface in a single direction, while diffuse reflection is when light reflects off a rough surface in many different directions.
• If a coloured object is opaque:out of the incident white light onlya certain colour light (e.g purple light) is reflected, all other colours are absorbed.
• Filters:-All other colours are absorbed, and only a certain colour is allowed to pass through - so onlya certain wavelength is transmitted through the filter
• What is a diverging lens?

  A lens that causes parallel light rays to spread out or diverge. (They are concave)

  
• What is a converging lens?


  A lens that causes parallel rays of light to converge at a focal point. (They are convex).

  
• All electromagnetic waves are transverse, and they travel at the same speed in a vacuum.
• A diverging lens always produces a virtual image and it is on the same side of the real image on the same side of the object.

  
• This is a diagram about converging lenses:


  This is a diagram about converging lenses:

  
• All Electromagnetic waves transfer energy from source to absorber. For example, infrared waves transfer energy from a heater to a hot object using infrared waves.
• What is the practical used to investigate refraction?

  Setup:

  Use a glass block to study air-glass refraction.

  Procedure:

  Trace incident/emergent rays, draw refracted path.

  Draw normal at entry, measure angles.

  Repeat 3 times with constant angle of incidence.

  Calculation:

  Use protractor, calculate average angles.

  Concepts:

  Understand air-glass refraction.

  Follow systematic procedure.

  Outcome:

  Collect data on refracted light angles through the glass block.
• What are the main groupings of the electromagnetic spectrum?

  Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
• Radio waves have the longest wavelength and the lowest frequency while gamma rays have the shortest wavelength and highest frequency.
• our eyes can only detect a limited range of frequencies of electromagnetic radiation.
• Radio waves can go through the body without damaging anything.
• Infrared radiation may burn the skin if it gets too hot (the skin).
• Ultraviolet light may damage the skin and cause mutations if exposed for a long time. It could cause skin cancer.
• X-rays and gamma rays can cause cancer due to prolonged exposure as they are ionizing. They can cause mutations to the genes of the cells.
• different substances may absorb, transmit, refract, or reflect electromagnetic waves in ways that vary with wavelength.
• all bodies emit radiation, the intensity and wavelength distribution of any emission depends on their temperature.
• for a body to be at a constant temperature it needs to radiate the same average power that it absorbs.
• If Average Radiated Power is Less than Absorbed Power:

  The body gains more energy than it loses.

  The excess energy contributes to an increase in the body's internal energy.

  The body may experience a rise in temperature, leading to heating.

  If Average Radiated Power is More than Absorbed Power:

  The body loses more energy than it gains.

  The deficit in energy may result in a decrease in the body's internal energy.

  The body may cool down, and if the energy loss persists, it could lead to a decrease in temperature.
• The overall temperature of the earth is affected by the amount of radiation it reflects, absorbs, and emits. This is due to the atmosphere, clouds, and surface trapping the radiation emitted by the sun.
• What is the experiment for testing how much a surface absorbs energy?

  Wrap identical test tubes with different surfaces/colors (e.g., black, white, glossy, matte) using the same material.

  Fill each tube with boiling water and measure the water temperature every minute using a thermometer.

  Matte and black surfaces are expected to be better emitters; water temperature decreases faster in tubes with efficient radiation-emitting surfaces.

  Conclusion: Matte and black surfaces exhibit superior radiation emission compared to shiny or white surfaces.
• What is the use of radio waves?

  broadcasting, communications and satellite transmissions
• What is the use of microwaves?

  cooking, communications and satellite transmissions
• What is the use of infrared radiation?

  cooking, thermal imaging, short-range communications, optical fibers, television remote controls, and security systems
• What is the use of ultraviolet light?

  security marking, fluorescent lamps, detecting forged bank notes and disinfecting water
• What is the use of x-rays?

  observing the internal structure of objects, airport security scanners and medical x-rays
• What is the use of gamma rays?

  sterilising food and medical equipment, and the detection of cancer and its treatment
• Radio waves can be produced by or induce certain oscillations (frequency) that can be picked up by an antenna at a certain target range.