physics light and the elctromagnetic spectrum

What is a concave lens?

A lens that is thinner in the centre than at the edges.

What does a concave lens do to light?

It diverges light rays and spreads them out.

What is another name for a concave lens?

A diverging lens.

What happens to parallel rays passing through a concave lens?

They spread out as if they came from a virtual focal point.

How do you draw a ray diagram for a concave lens?

Draw a parallel ray to the lens then show it diverging away from the focal point on the same side as the object.

What is a convex lens?

A lens that is thicker in the centre than at the edges.

What does a convex lens do to light?

It converges light rays towards a focal point.

What is another name for a convex lens?

A converging lens.

What happens to parallel rays passing through a convex lens?

They converge at the principal focus on the opposite side of the lens.

How do you draw a ray diagram for a convex lens?

Draw a parallel ray that refracts through the focal point on the opposite side of the lens.

What is the principal focus of a convex lens?

The point where parallel rays converge after passing through the lens.

What is the principal focus of a concave lens?

The point from which diverging rays appear to originate.

What is the focal length of a lens?

The distance between the centre of the lens and its principal focus.

What is the relationship between lens shape and focal length?

A more strongly curved lens generally has a shorter focal length.

What is the power of a lens?

A measure of how strongly a lens converges or diverges light.

What is the equation for the power of a lens?

Power = 1 ÷ focal length.

What is the equation for lens power using symbols?

P = 1 ÷ f.

What unit must focal length be converted into when calculating lens power?

Metres.

What is the unit of lens power?

Dioptres (D).

What is the relationship between focal length and lens power?

A shorter focal length means a greater magnitude of lens power.

What is the sign of the power of a converging lens?

Positive.

What is the sign of the power of a diverging lens?

Negative.

What is the power of a lens with a focal length of 0.5 m?

2 dioptres.

What is the power of a lens with a focal length of 0.25 m?

4 dioptres.

What is a real image?

An image formed where light rays actually meet.

Where is a real image formed by a lens?

On the opposite side of the lens to the object.

Which type of lens can produce a real image?

A convex lens.

When does a convex lens produce a real image?

When the object is further from the lens than its focal length.

What is a virtual image?

An image formed where light rays appear to come from but do not actually meet.

Where does a virtual image appear to be formed?

On the same side of the lens as the object.

Which type of lens always produces a virtual image?

A concave lens.

When does a convex lens produce a virtual image?

When the object is closer to the lens than its focal point.

What type of image does a concave lens produce?

An upright smaller virtual image.

What type of image does a convex lens produce when the object is beyond its focal point?

An inverted real image.

What happens to an image when an object is inside the focal length of a convex lens?

The image is upright enlarged and virtual.

What are concave lenses used for?

Correcting short-sightedness.

Why are concave lenses used to correct short-sightedness?

They diverge light so it can be focused onto the retina.

Where is light focused in an eye with short-sightedness?

In front of the retina.

What are convex lenses used for?

Magnifying glasses binoculars and correcting long-sightedness.

Why are convex lenses used to correct long-sightedness?

They converge light so it can be focused onto the retina.

Where is light focused in an eye with long-sightedness?

Behind the retina.

What do all electromagnetic waves transfer?

Energy from a source to an absorber.

What type of waves are electromagnetic waves?

Transverse waves.

What does it mean that electromagnetic waves are transverse?

Their oscillations are perpendicular to the direction of energy transfer.

What speed do all electromagnetic waves travel at in a vacuum?

3 × 10^8 m/s.

Do electromagnetic waves need a medium to travel through?

No they can travel through a vacuum.

What is a vacuum?

A space containing no matter.

Do all electromagnetic waves travel at the same speed in a vacuum?

Yes they all travel at the speed of light.

What happens to electromagnetic waves when they enter a material?

They may be absorbed transmitted reflected or refracted.

Give an example of electromagnetic waves transferring energy.

Microwaves transfer energy from a microwave source to food.

How does the Sun transfer energy to the Earth?

Through electromagnetic radiation travelling through space.

What are the seven main groups of the electromagnetic spectrum in order of increasing wavelength?

Radio waves microwaves infrared visible light ultraviolet X-rays and gamma rays.

What are the seven main groups of the electromagnetic spectrum in order of increasing frequency?

Gamma rays X-rays ultraviolet visible light infrared microwaves and radio waves.

What is the order of the electromagnetic spectrum from longest to shortest wavelength?

Radio waves microwaves infrared visible light ultraviolet X-rays and gamma rays.

What is the order of the electromagnetic spectrum from lowest to highest frequency?

Radio waves microwaves infrared visible light ultraviolet X-rays and gamma rays.

Is the electromagnetic spectrum continuous or made of separate bands?

It is continuous but can be divided into groups.

What happens to frequency as wavelength decreases in a vacuum?

Frequency increases.

What happens to wavelength as frequency increases in a vacuum?

Wavelength decreases.

What is the relationship between wave speed frequency and wavelength?

Wave speed = frequency × wavelength.

What is the equation for electromagnetic wave speed?

c = f × λ.

What does c represent in the electromagnetic wave equation?

Wave speed in a vacuum.

What does f represent in the electromagnetic wave equation?

Frequency in hertz.

What does λ represent in the electromagnetic wave equation?

Wavelength in metres.

What happens to the energy of electromagnetic waves as frequency increases?

The energy of each photon increases.

Which electromagnetic waves have the lowest frequency?

Radio waves.

Which electromagnetic waves have the highest frequency?

Gamma rays.

Which electromagnetic waves have the longest wavelength?

Radio waves.

Which electromagnetic waves have the shortest wavelength?

Gamma rays.

What colours make up visible light in order of increasing frequency?

Red orange yellow green blue indigo and violet.

Which visible colour has the longest wavelength?

Red.

Which visible colour has the shortest wavelength?

Violet.

Which part of the electromagnetic spectrum can human eyes detect?

Visible light only.

Can human eyes detect all electromagnetic frequencies?

No they can only detect a limited range.

What is transmission of electromagnetic radiation?

When radiation passes through a material.

What is absorption of electromagnetic radiation?

When a material takes in energy from radiation.

What is reflection of electromagnetic radiation?

When radiation bounces off a surface.

What is refraction of electromagnetic radiation?

When radiation changes direction because its speed changes as it enters a different material.

How can different materials interact with electromagnetic waves?

They can absorb transmit reflect or refract them differently depending on wavelength.

Why can glass transmit visible light but absorb some ultraviolet radiation?

The material interacts differently with different wavelengths.

What happens to the speed of electromagnetic waves when they enter a different medium?

Their speed changes.

What happens to the frequency of an electromagnetic wave when it enters a different medium?

Its frequency stays constant.

What happens to the wavelength when an electromagnetic wave enters a different medium?

Its wavelength changes because its speed changes.

Why does an electromagnetic wave refract when entering a different medium?

Its speed changes at the boundary.

What happens to a light ray entering glass from air at an angle?

It slows down and bends towards the normal.

What happens to a light ray entering air from glass at an angle?

It speeds up and bends away from the normal.

What happens to a light ray entering a material along the normal?

Its speed changes but its direction does not.

What is the aim of the refraction core practical?

To investigate how electromagnetic waves interact with a rectangular glass block.

What equipment is used in the glass block refraction practical?

A rectangular glass block paper pencil ruler protractor and ray box.

How do you investigate refraction through a glass block?

Trace the block shine a narrow ray of light into it and record the path of the ray.

How do you measure the angle of incidence?

Measure the angle between the incoming ray and the normal.

How do you measure the angle of refraction?

Measure the angle between the refracted ray and the normal.

What is the normal in a refraction experiment?

An imaginary line at 90 degrees to the surface.

What happens when light enters glass from air?

It slows down and bends towards the normal.

What happens when light leaves glass and enters air?

It speeds up and bends away from the normal.

Why does light change direction when it enters glass?

Its speed changes because it enters a different medium.

What happens to the ray when it leaves a rectangular glass block?

It emerges parallel to the incident ray but displaced sideways.

What is lateral displacement?

The sideways shift between the original path of a ray and its emerging path.

Why should a narrow ray of light be used?

It makes the path of the light easier to identify accurately.

How can you improve the accuracy of the refraction practical?

Use a narrow ray and measure angles carefully from the normal.

What do all bodies emit?

Electromagnetic radiation.