Question

1. why are audio recording halls covered with soft materials (2 marks)

1. state the property of sound that makes a bat fly safely in complete darkness (1 mark)

1. a man is standing \\(85\text{ m}\\) from a cliff face infront and \\(170\text{ m}\\) from a cliff face at his back. he whistles loudly and hears two echoes, one after another

(i) explain how this can happen (1 mark)
(ii) calculate the time interval between the two echoes. (velocity of sound in air = \\(340\text{ ms}^{-1}\\)) (3 marks)

1. state one factor that affects the velocity of sound in air. (1 mark)

1. give an expression which can be used to calculate electrical energy. (1 mark)

1. state one advantage of a pinhole camera over lens camera (1 mark)

Explanation:

🆕 New Concept Discovered: Echo and Sound Reflection
How sound waves bounce off barriers to create echoes.

Step 1: Solve Question 7 (Audio Recording Halls)

Soft materials are porous and contain air pockets. When sound waves hit these materials, the sound energy is absorbed and converted into heat energy rather than being reflected. This prevents reverberation (multiple reflections or echoes), ensuring clear audio recordings.

Step 2: Solve Question 8 (Bat Flight)

Bats use reflection of sound (specifically, ultrasonic waves or echolocation) to navigate. They emit high-frequency sound waves that bounce off obstacles and return to their ears, allowing them to detect the position of objects in the dark.

Step 3: Solve Question 9(i) (Two Echoes Explanation)

The sound waves from the whistle travel in opposite directions towards both cliffs. Since the two cliffs are at different distances from the man (\(85\text{ m}\) and \(170\text{ m}\)), the sound waves take different amounts of time to travel to each cliff and reflect back to his ears. This results in two distinct echoes heard at different times.

Step 4: Solve Question 9(ii) (Time Interval Calculation)

An echo travels to the cliff and back, covering twice the distance (\(2d\)).

The time \(t\) taken for an echo to return is given by:

$$t = \frac{2d}{v}$$

where \(v = 340\text{ m/s}\).

• First echo from the closer cliff (\(d_1 = 85\text{ m}\)):

$$t_1 = \frac{2 \times 85}{340} = \frac{170}{340} = 0.5\text{ s}$$

• Second echo from the farther cliff (\(d_2 = 170\text{ m}\)):

$$t_2 = \frac{2 \times 170}{340} = \frac{340}{340} = 1.0\text{ s}$$

• Time interval between the two echoes (\(\Delta t\)):

$$\Delta t = t_2 - t_1 = 1.0\text{ s} - 0.5\text{ s} = 0.5\text{ s}$$

Step 5: Solve Question 10 (Velocity of Sound in Air)

The velocity of sound in air is affected by several factors. One primary factor is temperature (as temperature increases, the speed of sound increases). Other acceptable factors include humidity or wind direction/speed.

Step 6: Solve Question 11 (Electrical Energy Expression)

Electrical energy (\(E\)) can be calculated using the formula:

$$E = VIt$$

where:

• \(V\) = Voltage (Potential Difference)
• \(I\) = Current
• \(t\) = Time

(Alternative correct expressions include \(E = I^2Rt\) or \(E = \frac{V^2}{R}t\))

Step 7: Solve Question 12 (Pinhole Camera Advantage)

One major advantage of a pinhole camera over a lens camera is that it has an infinite depth of field, meaning all objects, whether near or far, are in focus at the same time without needing any adjustment. Another advantage is that it produces images free from lens distortions or aberrations.

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Answer:

• 7. Soft materials absorb sound waves instead of reflecting them, preventing echoes and reverberations to ensure clear recordings.
• 8. Reflection of sound (or Echolocation / Ultrasound reflection).
• 9. (i) The two cliffs are at different distances from the man, so the reflected sound waves (echoes) take different amounts of time to travel back to him.
• 9. (ii) \(0.5\text{ seconds}\)
• 10. Temperature (or Humidity).
• 11. \(E = VIt\) (where \(V\) is voltage, \(I\) is current, and \(t\) is time).
• 12. It has an infinite depth of field (all objects near and far are in focus simultaneously) and produces images free from lens distortion.