Practice Questions for Year 11 Physics Module 3: Waves and Thermodynamics

Question 6 ⭐⭐

Define resonance and provide an example to help explain your answer.

Sound Waves

Question 7 ⭐

Scientists wishing to measure the current distance from the Earth to the Moon fired a laser from their observatory to a retroreflector placed on the moon. They recorded the time taken for the laser to return to Earth as 2.6932s. How far away is the moon?

Question 8 ⭐⭐

A bystander notices that when stationary, the frequency of a police siren is 1800Hz. What would the frequency of the siren be if a bystander approaches the police car at 2ms^-1, and the police car approaches the bystander at 20ms^-1?

Question 9 ⭐⭐⭐

Initially a wave with wavelength 35cm passes through a gap in a barrier that is 30cm wide, a moderate amount of diffraction is observed. State what would be observed if the frequency of the wave was increased whilst keeping the gap width constant.

Question 10 ⭐⭐⭐⭐

A tuned violin ‘A’ string will play at 44oHz – its resonant frequency – the player then changes notes, and puts their finger into second position, the violin now plays a different note – and also the resonant frequency. Why is this possible?

Question 11 ⭐

A bus passenger notices that while stopped at a red light, the window on the bus vibrates quite significantly. However when the bus is in motion, the passenger cannot notice any vibration in the window. Explain why this occurs.

Question 12 ⭐⭐

A person by a railway line listens for an oncoming train by putting their ear to the track. Why does this method give an earlier warning of the approach of a train than just standing around and listening?

Ray Model of Light

Question 13 ⭐⭐⭐⭐

Explain differences in image formed by a concave and convex lens. Use diagrams to strengthen your answer.

Question 14 ⭐⭐⭐

Create an expression for the critical angle of a substance and the relative refractive index of the boundary involved in the interaction using Snell’s law.

Question 15 ⭐⭐

What is total internal reflection?

Question 16 ⭐⭐⭐⭐

How does the inverse square law for electromagnetic radiation help us in our ability to study our Universe?

Thermodynamics

Question 17 ⭐⭐

A scientist is given an unknown metallic substance and is asked to find its specific heat capacity. They determine that it has a weight of 30N and observe that 1.5 x 10⁴J raises the substances temperature by 22°C. What is the substance’s specific heat capacity?

Question 18 ⭐⭐

Two metal squares of the same material have a surface area of 3m2 and 6m2. The two squares are heated evenly in the same environment and have the same thickness. Predict the rate at which each square loses energy as it becomes cooler. Justify your answer.

Question 19 ⭐⭐⭐

A house has 200 m2 worth of windows that are 2.5 mm thick. The glass has a thermal conduction constant of 0.75 Wm-1K-1. If the outside temperature is -5ºC and the internal temperature is 27ºC, how much energy is transferred via the windows per hour?

Question 20 ⭐⭐⭐⭐

0.1kg of liquid ethanol at -15°C (specific heat capacity of 2428 J/kg K) is poured into a glass cylinder at 20°C (with specific heat capacity of 840 J/kg K) with mass 0.15kg. What is the thermal equilibrium temperature?

Question 1

Sample Answer:

The mathematical relationship between frequency and wavelength is v = f x l and since both waves are travelling at the same speed, at the same frequency, then they must have the same wavelength. 

💡Tip: Remember that there are a lot of equations in physics and it is not necessary to memorise all of them – I did not memorise any of them (other than the ones that came up often enough to become second nature). 

Utilise the formula sheet and know where each of the formulae are, so that you don’t waste time on the exam looking for the appropriate formula for a question like this.

Question 2

Sample Answer: 

💡Tip: Remember your SI units and significant figures for your answers to mathematical physics questions.

Question 3

Sample Answer:

800Hz

💡Tip: Now, this was a trick question because there is no working out. Rather, it asks you to go back to your fundamental understanding of waves and what they are. When a sound wave moves from one medium to another it will alter in speed, unlike an electromagnetic wave. However, this change in speed is a result of a change in wavelength not frequency. So the frequency remains the same, but the wavelength will change therefore causing a change in the speed (due to v = f x l). 

Question 4

Sample Answer:

a)

b)

The lasers emit light outside the visible spectrum (approx 400 – 700nm) and therefore, cannot be seen. 

c)

One laser is emitting infrared light, which heats up the person’s arm. The second laser is emitting UV light, which does not heat the person’s arm, but essentially gives the exposed portion of the skin a sunburn. 

💡Tip: A reminder to convert all units to SI units before putting it in the formula (such as in part a). Convert nanometers to meters before solving the equation.

Question 5

Sample Answer:

700Hz. 

💡Tip: This was another trick question to see if you were paying attention earlier! See my tips for Question 3. 

Question 6

Sample Answer:

Resonance is the natural phenomenon where an external force applied to an object will result in the object amplifying its oscillations. A daily example observed is when an individual is swinging on a swing and another person pushes them from behind. This results in the frequency of the oscillations to increase and therefore resonance has occurred to allow the swing to go at a faster pace. 

💡Tip: Another example that students may want to look into is the ‘Tacoma Narrows Bridge’ which illustrates how forced resonance by the force of air resulted in its collapse.

Question 7

Sample Answer:

Question 8

Sample Answer:

💡Tip: This question requires the use of the Doppler Equation, which is easy to use once you have drawn out the diagram – remember to denote which direction is positive and negative (in this case, moving to the right is positive, whilst moving to the left is negative).

Question 9

Sample Answer:

The amount of diffraction observed would increase as the frequency increases, and the wavelength decreases until it is about the same size as the width gap. As the frequency continues to increase past this point, the wavelength would continue to decrease and the degree of diffraction would decrease until the wavelength is too small to cause any diffraction.

Question 10

Sample Answer:

Placing a finger onto the violin string shortens the amount of string that can vibrate, effectively changing the characteristics of the string. It will thereby vibrate at a higher pitch and at a different resonant frequency. 

Question 11

Sample Answer:

While the bus is stopped, the engine is operating at a frequency near the resonant frequency of the windows or other elements of the bus causing them to vibrate significantly. When in motion, the engine changes this frequency and it is no longer operating around the resonant frequency. 

Question 12

Sample Answer:

The speed of sound through the ground/ railway tracks will be much faster than the speed of sound through air as the molecules are more tightly packed and therefore, can transmit the sound faster.

Question 13

Sample Answer:

Concave lenses result in the divergence of rays outwards, whilst convex lenses result in the convergence of the rays in towards a focal point. In a concave lens, the image formed will be smaller, but upright and will not be ‘real’. This is because the image is placed between the object and the lens, and therefore cannot be observed directly. On the other hand, an upright, real image will form in a convex lens, but its size will be dependent upon the position at which the object is placed between the focal point and the lens. 

Tip💡: As a point of interest, you might want to research how this applies to vision and vision corrective measures (e.g. spectacles – which lenses are better to correct myopia or hyperopia). 

Question 14

Sample Answer:

The critical angle is one in which the incident ray, upon encountering a boundary will refract to follow the line of the boundary instead.

Question 15

Sample Answer:

Total internal reflection arises as a consequence of refraction. As the wave is travelling from a high refractive index medium to a low refractive index medium, the amount of refraction can be so great that the wave does not refract at all, instead being reflected by the boundary layer.

Question 16

Sample Answer:

The inverse square law states that there is an inverse square proportionality relationship between intensity and radius/ distance (i.e. as the distance increases the intensity decreases). According to the Big Bang Theory, when the universe was created from that point of singularity, there was rapid expansion of the universe, which also resulted in the release of electromagnetic radiation. As the universe expanded, the distance continued to increase which therefore resulted in a decrease in the intensity of the electromagnetic radiation. This is now captured as cosmic radio waves and have provided evidence for the Big Bang Theory.

💡Tip: This question uses your knowledge back from year 10, so don’t stress if you don’t quite remember the answer. You will go over it again in Year 12!

Question 17

Sample Answer:

Question 18

Sample Answer:

To answer this question, the thermal conductivity equation will be utilised, as follows: 

As observed, there is a direct proportional relationship between the surface area and the energy gained/ lost per unit time (Q/t). So as the surface area increases, the energy lost to the environment will also increase. Thus, the rate at which the 6m2 block will be twice/ 2x the rate of the 3m2 block thickness. 

💡Tip: Proportionality questions are some of the harder style questions that students tend to make mistakes in. Just remember to look at what are the constants and then focus on the relationships between the changing variables.

Question 19

Sample Answer:

💡Tip: Important to note the units that are being used: 

• Convert the 2.5mm to metres
• Final answer should be in joules/ hour NOT joules/ second

Question 20

Sample Answer: