Scottish National 5 (Nat 5) Physics Flashcards

24 sample cards from the Physics deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. What is the difference between a transverse and a longitudinal wave? Give an example of each.

   In a transverse wave the particle vibrations are perpendicular to the direction of energy travel (e.g. light, water waves). In a longitudinal wave the vibrations are parallel to the direction of travel (e.g. sound).

2. List the regions of the electromagnetic spectrum in order of increasing frequency.

   Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. (Increasing frequency means decreasing wavelength.)

3. What do all members of the electromagnetic spectrum have in common?

   They are all transverse waves, are all forms of electromagnetic radiation, and all travel at the same speed in a vacuum, $3 \times 10^{8}\ \text{m s}^{-1}$.

4. Give a typical detector and a use for radio waves and for infrared.

   Radio waves: detected by an aerial/radio receiver; used for communication/broadcasting. Infrared: detected by a thermometer/thermal camera; used for heating and thermal imaging.

5. Define refraction of light.

   Refraction is the change in speed (and usually direction) of light as it passes from one medium into another of different optical density.

6. When light passes from air into glass, what happens to its speed, wavelength, frequency and direction?

   Speed decreases, wavelength decreases, frequency stays the same, and the ray bends towards the normal (because it slows down on entering the denser medium).

7. Define the angle of incidence and the angle of refraction.

   Both are measured from the normal (the line perpendicular to the surface). The angle of incidence is between the incident ray and the normal; the angle of refraction is between the refracted ray and the normal.

8. What are the three types of nuclear radiation, and what is each made of?

   Alpha ($\alpha$): a helium nucleus (2 protons + 2 neutrons). Beta ($\beta$): a fast-moving electron. Gamma ($\gamma$): high-frequency electromagnetic radiation (a photon).

9. Compare the ionising power and penetrating ability of alpha, beta and gamma radiation.

   Alpha: most ionising, least penetrating (stopped by paper/skin). Beta: medium ionising, medium penetrating (stopped by a few mm of aluminium). Gamma: least ionising, most penetrating (reduced by thick lead/concrete).

10. Define activity of a radioactive source and give its equation and unit.

    Activity is the number of nuclear decays per second: $A = \dfrac{N}{t}$, measured in becquerels (Bq), where 1 Bq = 1 decay per second.

11. Define absorbed dose and equivalent dose, with their equations and units.

    Absorbed dose: $D = \dfrac{E}{m}$, energy absorbed per kg, in grays (Gy). Equivalent dose: $H = Dw_R$ (absorbed dose $\times$ radiation weighting factor), in sieverts (Sv).

12. Define half-life of a radioactive source.

    The half-life is the time taken for the activity (or the number of undecayed nuclei) of a radioactive source to fall to half of its original value.

13. A source has a half-life of 6 hours and an initial activity of 800 Bq. What is its activity after 18 hours?

    18 hours is 3 half-lives. Each half-life halves the activity: $800 \to 400 \to 200 \to 100$. The activity is $100\ \text{Bq}$.

14. Distinguish between average (scalar) speed and (vector) velocity.

    Speed is a scalar: distance travelled per unit time, $\bar{v} = \dfrac{d}{t}$. Velocity is a vector: displacement per unit time, $v = \dfrac{s}{t}$, and has both magnitude and direction.

15. Define acceleration and give its equation with units.

    Acceleration is the rate of change of velocity: $$a = \frac{v - u}{t},$$ where $u$ is initial velocity, $v$ is final velocity (m s$^{-1}$), $t$ is time (s); $a$ is in m s$^{-2}$.

16. On a velocity–time graph, what do the gradient and the area under the line represent?

    The gradient (slope) represents the acceleration; the area under the line represents the displacement (distance travelled).

17. State Newton's first law of motion.

    An object remains at rest, or continues to move at a constant velocity (constant speed in a straight line), unless acted on by an unbalanced (net) force.

18. State Newton's second law and give its equation.

    The unbalanced force on an object equals the product of its mass and acceleration: $F = ma$, where $F$ is in newtons (N), $m$ in kg and $a$ in m s$^{-2}$.

19. State Newton's third law of motion.

    If object A exerts a force on object B, then B exerts an equal in size and opposite in direction force on A. (Forces always occur in action–reaction pairs.)

20. What is meant by the resultant (unbalanced) force on an object, and how are two perpendicular forces combined?

    The resultant is the single force equivalent to all forces acting. Two perpendicular forces combine by Pythagoras: $$F_R = \sqrt{F_x^{2} + F_y^{2}}.$$

21. Explain why an object reaches terminal velocity when falling through air.

    As speed increases, air resistance increases until it balances the weight. The forces are then balanced, the unbalanced force is zero, so acceleration is zero and the object falls at a constant (terminal) velocity.

22. Describe the motion of a projectile in terms of its horizontal and vertical components.

    Horizontal motion: constant velocity (no horizontal force, ignoring air resistance). Vertical motion: constant acceleration downward due to gravity ($g$). The two components are independent.

23. For a satellite in circular orbit, why does it stay in orbit even though gravity acts on it?

    Gravity provides the central (centripetal) force that continuously changes the satellite's direction. The satellite has a high enough horizontal speed that it constantly "falls" towards Earth while curving past it, maintaining its orbit.

24. Define weight and give its equation, distinguishing it from mass.

    Weight is the force of gravity on an object: $W = mg$, in newtons (N). Mass is the amount of matter (kg) and is constant, whereas weight depends on the gravitational field strength $g$ (N kg$^{-1}$), so it changes between planets.

What this deck covers

Physics flashcards FAQ