Physics (paper 1) đź“Ť Flashcards
What are the function of waves?
They transfer energy and information without transferring matter
Wavelength (λ)
Minimum distance in which a wave repeats itself
What is a wavelength measured in?
Metres
Amplitude (A)
Distance between the origin and the crest/trough
Frequency (f)
Number of waves that pass a point in a second
Frequency and wavelength are
inversely proportional
• High frequency = short wavelengths
• Low frequency = long wavelengths
How is the wavelength measured in transverse and longitudinal waves?
Transverse waves:
From one peak/crest to the next
Longitudinal waves:
From the centre of one compression to the next centre of compression
Time period (T)
The time taken for a single wave to pass a point
Wave velocity (speed)
The distance travelled by a wave each second
Transverse wave
Waves where the particles move perpendicular to the direction of energy transfer (oscillating motion)
Examples of transverse waves
• Ripples on the surface of water
• S - waves
• Electromagnetic waves (eg radio, light, x rays)
Longitudinal wave
Wave where the particles vibrate parallel to the direction of energy transfer (side to side motion)
What type of wave can travel through a vacuum?
Electromagnetic waves
When the points are close together in a longitudinal wave
Compression
When the points are spaced apart in a longitudinal wave
Rarefaction
Examples of longitudinal waves
• Sound waves
• P - waves
• Ultrasound
• Infrasound
Equations for wave speed (m/s)
• v = x/t
(Wave speed = distance/time)
• v = f x λ
(Wave speed = frequency x wavelength)
How do you work out wavelength? (λ)
Length x 2
Seismic wave
Wave produced by earthquakes
Types of wave interactions through an interface
• Reflection
• Refraction
• Transmission
• Absorption
Materials interact differently with waves depending on the wave’s ______
wavelength
Reflection definition
The bouncing back of a wave at a boundary
Refraction definition
When a wave changes speed at the boundary between materials of different densities
Transmission definition
When a wave passes through a substance
Absorption definition
When energy is transferred from the wave to the particles of a substance
What’s an echo?
Sound waves being reflected off a surface
How do waves get reflected?
(effect)
• Flat surfaces are the most reflective
(The smoother the surface, the stronger the reflected wave)
• Light will reflect if the object is opaque
• Electrons absorb the light energy and re emit it as a reflected wave
What does it mean if an object appears yellow?
• Only yellow light has been reflected
• All other wavelengths of visible light have been absorbed
What happens when waves speed up?
• The frequency stays the same
• The wavelength increases (gets longer)
• The waves travel away from the normal
What happens when waves slow down?
• The frequency stays the same
• The wavelength decreases
• The waves travel toward the normal
What is a normal
A line drawn perpendicular to an interface
Sound waves definition
The vibrations of molecules
Regions of higher and lower density in a longitudinal wave
Higher density: Compression
Lower density: Rarefaction
Range of frequencies humans can hear
20 Hz to 20,000 Hz
Ultrasound
Sound waves with a frequency above the human hearing range of 20000 Hz
Infrasound
Sound waves with a frequency below the human hearing range of 20 Hz
Explain the way the human ear works
• Vibrations in the air travels down the auditory canal causing the eardrum to vibrate
• Vibrations are passed onto the three small bones
• These bones amplify vibrations and transmit them to the liquid in the cochlea
• Tiny hairs in the cochlea detect vibrations and create electrical impulses
• They travel along neurones in the auditory nerve to the brain
Incident angle
Angle of the entering ray
What is the angle of reflection?
The angle of the exiting ray
Can sound waves travel through a vacuum? Explain.
• No. Longitudinal waves rely on vibrating particles to travel
• In a vacuum there are no particles to vibrate, and so sound waves can’t be transmitted.
How is ultrasound used in sonar?
• Ultrasound is emitted from a boat and travels towards the sea bed
• Ultrasound reflects off the sea bed and is detected by the boat
• The time between emission and detection is recorded
• This can be used to find out the depth of seabed
Ultrasound uses
• Foetal scanning
• Sonar
• echo location
Infrasound uses
• Exploration of the Earth’s core
• Detecting seismic activity
How is ultrasound used for foetal scanning?
• A transducer produces and detects a beam of ultrasound waves in body
• Ultrasound waves are bounced back to the transducer by different boundaries
• The echo reaches the transducer causing it to generate electrical signals to send to the scanner
• The detector calculates the tissue’s distance from transducer using speed and time
• Time measurements are used to build up an image
Why is ultrasound a safe method for foetal scanning compared to eg X rays?
• x rays are ionising whereas ultrasound isn’t
• Therefore x rays could damage tissue and mutate cells
What is applied during foetal scanning and why?
Gel is applied to ensure ultrasound is absorbed not reflected off your body
How is infrasound used in the exploration of the earths core?
• Earthquakes produce P-waves and S-waves
• These pass through the Earth’s centre and can be detected using seismometers
• The location and magnitude can be identified after carefully timing the arrival of its waves
Characteristics of P-waves
Primary waves
• Longitudinal waves
• Faster than S-waves so are felt first during an earthquake
• Produce a forward and back motion
• Can pass through solids and liquids
• Are very low frequency sound waves (infrasound)
Characteristics of S-waves
Secondary waves
• Transverse waves
• Slower than P-waves so are felt after them during an earthquake
• Produces a side to side motion
• Can only travel through solids
• Unable to travel through the Earth’s molten outer core
Method to calculate wave speed by measuring the frequency
• Measure the frequency by counting the number of waves that pass a ping on the harbour each second
• Measure the wavelength by counting the number of waves between two point on the harbour and dividing the distance by the number of waves
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Concave meaning
Curving inwards
Convex meaning
Curving outwards
Focal length
The distance between the centre of the lens and the focal point
Real image
An image that is formed where the rays of light are focused and come together
Virtual image
An image where rays of light appear to come but don’t in reality
Incident ray
Light ray moving towards a boundary
Law of reflection
Angle of incidence is equal to the angle of reflection