Semester Two:

Year 9 Exam Notes Solutions Sound and Light, Heat and Electricity and Ecology

Sound and Light Reference Ch9

A wave is able to transmit energy from one place to another without moving any matter over the same distance. There are two different types of waves. Transverse and longitudinal (compression) waves.

Transverse wave vibrations or movement of the particles within the wave always travel PERPENDICULAR to the direction of travel. Longitudinal wave vibrations move always PARALLEL to the direction of travel.

A WAVELENGTH of a wave is the distance between two crests, or two troughs, or the distance between any two corresponding points on neighbouring waves. It is measured in meters and is given

the symbol lambda (λ). The number of complete vibrations or waves made in one second is referred to as the FREQUENCY. It is measured in Hertz (Hz) and one hertz is equal to one vibration per second. The AMPLITUDE of a wave is the maximum distance that each particle moves away from its usual resting position.

Label the missing terms on the diagram below, describing the length of each:

WAVELENGTH – 6cm

AMPLITUDE – 2cm

Classify each wave below as either a transverse or longitudinal wave, give descriptions for the X and Y in the diagram.

X = COMPRESSION

Y = RAREFACTION

The speed or velocity of a wave can be calculated using the following wave equation:

V = f λ

V = velocity (m/s)

f = frequency (Hz)

λ = wavelength (m)

The frequency of a wave is inversely proportional to the period of the wave. The period of a wave is the time for a particle on a medium to make one complete vibrational cycle and is measured in seconds.

The relationship between frequency and period can be seen in the following equation:

Practice questions:

A wave is introduced into a thin wire held tight at each end. It has an amplitude of 3.8 cm, a frequency of 51.2 Hz and a distance from a crest to the neighbouring trough of 12.8 cm. Determine the period of such a wave.

Answer: 0.0195 sec

Here is an example of a problem with a lot of extraneous information. The period is simply the reciprocal of the frequency. In this case, the period is 1/(51.2 Hz) which is 0.0195 seconds.

Olivia accompanies her father to the park for an afternoon of fun. While there, she hops on the swing and begins a motion characterized by a complete back-and-forth cycle every 2 seconds. The frequency of swing is _________.

a. 0.5 Hz b. 1 Hz c. 2 Hz

Answer: A

Frequency refers to the number of occurrences of a periodic event per time and is measured in cycles/second. In this case, there is 1 cycle per 2 seconds.

So the frequency is 1 cycles/2 s = 0.5 Hz.

James and Tahlia stand 8 meters apart and demonstrate the motion of a transverse wave on a slinky. The wave e can be described as having a vertical distance of 32 cm from a trough to a crest, a frequency of 2.4 Hz, and a horizontal distance of 48 cm from a crest to the nearest trough. Determine the amplitude, period, and wavelength and speed of such a wave.

Amplitude = 16 cm

(Amplitude is the distance from the rest position to the crest position which is half the vertical distance from a trough to a crest.)

Wavelength = 96 cm

(Wavelength is the distance from crest to crest, which is twice the horizontal distance from crest to nearest trough.)

Period = 0.42 s

(The period is the reciprocal of the frequency. T = 1 / f)

Speed = 230 cm/s

(The speed of a wave is calculated as the product of the frequency times the wavelength.)

For notes on hearing, refer back to previous notes given in class.

Although loudness can be a matter of opinion, the disturbances in the air can be measured. The measurement is called the RELATIVE INTENSITY (SOUND LEVEL) and is measured in decibels (dB). The smallest sound level that can be heard when the air is vibrating is called the THRESHOLD OF HEARING. Whereas the smallest sound that causes pain is called the THRESHOLD OF PAIN.

Q. Complete the following table to describe some of the important structures of the ear.

Structure Description Purpose Eardrum A thin flap of skin

Vibrates in response to the vibrating air particles

Ossicles (or hammer, anvil and stirrup)

Three small bones in the middle ear

Passes on the vibrations from the middle ear to the inner ear

Oval window An opening into the inner ear Allows vibrations to pass into the cochlea

Cochlea A spiral-shaped system of tubes full of fluid

Contains receptor cells for hearing

Eustachian tube A canal from the middle ear to the throat (pharynx)

Allows air to move between the middle ear and the mouth and nose.

The electromagnetic spectrum refers to the many types of radiation released from stars, including our own sun. All radiation types move in waves. They all have particular things in common, such as travelling at the speed of light in a vacuum and they can all be reflected, refracted and diffracted. It is the frequency and wavelength that changes.

Label the missing types of radiation in the following diagram and describe the size of their frequency and wavelength:

There are some differences between sound and electromagnetic waves. For instance, all electromagnetic waves are TRANSVERSE, whereas sound waves are LONGITUDINAL (COMPRESSION). The speed of electromagnetic waves is greater than/slower than sound waves. Sound waves can travel in SOLID, LIQUID, GAS but not VACUUM.

Light:

Light travels in straight lines as it travels through empty space or in a uniform medium such as air and water. The lines that are used to show the path of light are called RAYS. A collection of these are referred to as a BEAM of light.

When light meets a boundary between two different substances many things can happen:

Light can bounce off the surface of an object or substance, this is called REFLECTION and the angle at which the light enters is the same angle at which it is REFLECTED. This is known as the Law of REFLECTION.

If most of the light travels through a substance then the surface is called TRANSPARENT. An example of this type of surface would include GLASS.

Some objects only let just enough light through in order to detect shapes of objects on the other side, this type of surface is referred to as TRANSLUCENT. An example of this type of surface would include FROSTED GLASS.

Light can also be completely absorbed or reflected by the substance, transferring its energy to the particles in the substance. These types of surfaces are known as OPAQUE. An example of this type of surface is WOOD.

When light travels from one substance into another that is transparent or translucent it can slow down or speed up. This change in speed of light when traveling from one substance to another is called REFRACTION. It causes light to bend towards the normal which is a line that is at right angles to the boundary of the two substances.

When light speeds up, as it does when travelling from water to air, it bends AWAY FROM the normal.

When light slows down, as it does when travelling from air to water, it bends TOWARDS the normal.

Q. Describe whether, in the diagram, light would be speeding up or slowing down. Provide a reason.

LIGHT IS TRAVELLING FROM WATER TO AIR AND BENDING AWAY FROM THE NORMAL. IT IS THEREFORE, SPEEDING UP AS IT LEAVES THE WATER.

Lenses and Mirrors:

Flat mirrors – when light hits a flat mirror it reflects at the same angle from which it entered. All of the reflected light appears to be coming from the same point behind the mirror and that’s exactly where the image is. The object appears to be at the same distance behind the mirror as the real object is in front of the mirror.

Draw a diagram showing how light is reflected from a flat mirror.

Concave mirrors – A concave mirror is curved INWARDS. Light reflecting of a concave mirror converge/diverge to a focal point. Indicate where the focal point will be on the diagram below.

Convex mirrors – A convex mirror is curved OUTWARDS. Light reflecting of a convex mirror converge/diverge to a focal point. Indicate where the focal point will be on the diagram below.

Converging lens – This type of lens is the same lens that is in each of your eyes. Its shape is biconvex meaning that it is curved outwards on both sides.

Diverging lens – This lens spreads light outwards because of its biconcave shape. A biconcave lens does not have a real focal point. Instead it has a virtual focal point.

Q. Describe the type of lenses below and draw the path of the beams of light to show their focal points.

The exact shape of the clear jelly-like lens in your eye is controlled by muscles called ciliary muscles. These muscles relax and contract to change the shape of the lens. This process is called ACCOMODATION.

An endoscope is a long flexible tube that is used in medical examinations. Inside are two bundles of narrow glass strands called OPTICAL FIBRES. The glass inside is made so that light is unable to emerge from the glass and is reflected back into it. This process is called TOTAL INTERNAL REFLECTION.

Heat and Electricity Reference Ch10

The transfer of heat through a substance as a result of neighbouring vibrating particles is referred to as CONDUCTION. The particles in the region of high temperature vibrate more quickly than those in a lower temperature region, they therefore have more KINETIC ENERGY.

The particles move and bump into other particles passing on this energy. This continues until all particles have the same temperature.

Materials that are poor conductors are called INSULATORS. Some examples of poor conductors are:

1. FOAM 2. WOOL 3. FIBREGLASS

Q. Give a reason why the above materials are poor conductors.

THEY CONTAIN POCKETS OF AIR AND AIR IS A VERY POOR CONDUCTOR OF HEAT.

In liquids and gases, these particles are able to move when heated in order to pass on their energy to other molecules through collisions. This type of heat transfer is called CONVECTION. Describe the process happening in the diagram below. What is this process called?

THESE GAS PARTICLES ARE ABLE TO MOVE AROUND ONCE THEY OBTAIN KINETIC ENERGY FROM HEAT. THEY THEN COLLIDE WITH OTHER MOLECULES TO PASS ON THE KINETIC ENERGY. HOWEVER, AS PARTICLES MOVE AWAY FROM THE HEAT SOURCE THEY COOL AND LOSE ENERGY AND BECOME CLOSER TO EACH OTHER.

Heat can be transferred without the use of particles, such as electromagnetic waves. This type of heat transfer is referred to as RADIATION. Like all electromagnetic waves, they can be reflected, transmitted or absorbed depending on the material it comes into contact with.

Q. In the diagram below, explain whether the surface of the material heats up slowly or quickly, providing reasons for each.

CLEAR OBJECTS ALLOW LIGHT AND RADIANT HEAT TO PASS THROUGH THEM. THE TEMPERATURE DOES NOT INCREASE QUICKLY WHEN HEAT RECHES THEM BY RADIATION.

DARK OBJECTS TEND TO ABSORB LIHGT AND RADIANT HEAT. THEIR TEMPERATURE WOULD INCREASE QUICKLY.

SHINY OBJECTS TEND TO REFLECT LIGHT AND HEAT AWAY. THE TEMPERATURE OF THESE OBJECTS DO NOT CHANGE QUICKLY.

An electrical circuit involves the movement of ELECTRONS. Electric charge that does not move within a circuit and can be built up on certain surfaces is known as STATIC ELECTRICITY. The substances that do not allow electrical charge to pass through them quickly are called INSULATORS.

All electrical circuits need three things:

1. POWER SUPPLY 2. LOAD 3. CONDUCTING PATH

Q. Draw a circuit diagram of the above three essential items needed for a circuit.

Q. What is electric current? What does it measure?

ELECTRIC CURRENT IS THE FLOW OF ELECTRIC CHARGE WITHIN THE CIRCUIT. IT MEASURES THE AMOUNT OF ELECTRIC CHARGE PASSING A PARTICULAR POINT IN AN ELECTRIC CIRCUIT PER SECOND.

Q. What is voltage? What does it measure? Is it different to potential difference?

VOLTAGE IS A MEASURE OF THE AMOUNT OF ELECTRICAL ENERGY GAINED OR LOST BY ELECTRICAL CHARGE AS IT MOVES THROUGH THE CIRCUIT. VOLTAGE IS ALSO KNOWN AS PTOTENTIAL DIFFERENCE BECAUSE IT MEASURES A CHANGE IN THE POTENTIAL OR STORED ENERGY OF CHARGE.

Q. Name the following circuit symbols.

Series and Parallel circuits:

In series circuits, light globes are connected to the same conducting pathway. This means that when calculating the voltage, the voltage across each light globe will be the same/divided amongst them.

In parallel circuits, light globes have their own separate conducting pathway. This means that when calculating the voltage, the voltage across each light globe will be the same/divided amongst them.

Q. Describe the differences of faulty light globes when connected in series and parallel.

SERIES – IF ONE LIGHT GLOBE IS FAULTY, THE OTHERS WON’T WORK

CONDUCTING PATH

TWO WIRES CROSSING EACH OTHER

RESISTOR

BATTERY

BATTERY (TWO BATTERIES IN SERIES)

LIGHT GLOBE

AMMETER

VOLTMETER

PARALELL – IF ONE LIGHT GLOBE IS FAULTY, IT WON’T EFFECT THE OTHERS.

Q. Identify which of the light globes in the diagram are connected in series and in parallel.

SERIES – B and C

PARALLEL – A and B, A and C

Q. Calculate the voltage drop of the light globes in the following diagrams. Show your working.

VOLTAGE DROP = 6V/ 2 LIGHT GLOBES = 3V EACH

VOLTAGE DROP = 6V EACH

Q. Consider the following circuit consisting of 3 lamps and 3 switches.

Predict which lamp(s) will light when: (a) Switches S1 and S2 are

closed L2 and L3 b) Switches S1 and S3 are

closed L1 and L3 (c) Switches S2 and S3 are

closed. NONE

Electrical RESISTANCE is a measure of how hard it is for the electrons to flow through part of a circuit. It limits the amount of electric current and determines how much energy is lost by an electric charge as it moves around a circuit. It is measured in ohms (Ω).

The following equation highlights this relationship:

This equation shows that if the voltage is doubled, the current is also doubled. This relationship is known as OHM’S LAW.

Q. What is the voltage drop across a 100 Ω resistor when the electric current flowing through it is measured at 250mA? Show your working.

V= IR

V = 250x10^-3 x 100

V = 25V

Q. Circuit A has 6 volts, Circuit B has 12 volts.

a) Calculate the current when both circuits have a resistance of 6 Ω.

Circuit A Circuit B

I = V/R I = 12 / 6

I = 6 / 6 I = 2A

I = 1A

b) Calculate the current when both circuits have a resistance of 12 Ω.

Circuit A Circuit B

I = V/R

I = 6 / 12 I = 12 / 12

I = 0.5 A I = 1A

c) Is the light bulb in brighter in circuit A or circuit B? Provide a reason for your answer.

THE LIGHT GLOBE IN CIRCUIT B WOULD BE BRIGHTER AS IT HAS MORE CURRENT FLOWING THROUGH THE CIRCUIT PROVIDING MORE ELECTRICAL ENERGY

Q. What happens to the current in a circuit if a 1.5V battery is replaced by a 9V battery?

THE CURRENT WOULD ALSO INCREASE

Ecosystems-Flow of Energy & Matter