Leaving Cert Physics Ordinary free practice questions with answers

Question 1 (50 marks) [Waves, motion, circuits, practical and solar energy]

(a) Waves are a way of transferring energy. (i) Which of these types of electromagnetic radiation has a lower frequency than red light? Underline your choice: gamma rays, microwaves, ultraviolet, X-rays. (ii) All electromagnetic waves travel at the same speed c in a vacuum. Using the Formulae and Tables booklet, or otherwise, state this value of c, rounded to four significant figures. (iii) A wave has a frequency of 25 Hz and a wavelength of 12 m. Calculate the speed of the wave. (iv) Calculate the period of the wave.

(a) Answer: (i) Microwaves. (ii) c = 2.998 × 10⁸ m s⁻¹. (iii) v = fλ = 25 × 12 = 300 m s⁻¹. (iv) T = 1 ÷ f = 1 ÷ 25 = 0.040 s.

• Approach: red light is in the middle of the spectrum; lower frequency means the radiation sits on the radio-wave side; use v = fλ and T =

• (i) In order of increasing frequency: radio waves, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays. Microwaves are below red light. 2 marks.

• (ii) From the booklet, c = 2.998 × 10⁸ m s⁻¹ (3.00 × 10⁸ to three significant figures). 2 marks.

• (iii) v = fλ = 25 Hz × 12 m = 300 m s⁻¹. 3 marks. (iv) T = 1 ÷ f = 1 ÷ 25 = 0.040 s. 3 marks.

(b) The graph shows how the displacement of a toy car from its starting point changes with time. The car moves in four stages: A, B, C and D. (i) Is speed a scalar or a vector quantity? (ii) In which stage is the car stationary? (iii) In which stage is the car moving fastest? Calculate its velocity in that stage. (iv) Calculate the velocity of the car in stage A. (v) Calculate the total distance travelled by the car, and state its displacement after 8 seconds. 0 2 4 6 8 10 12 0 1 2 3 4 5 6 7 8 time (s) displacement (m)

(b) Answer: (i) Scalar (it has magnitude only). (ii) Stage B (the graph is flat). (iii) Stage C, the steepest section: v = (10 − 4) ÷ (5 − 4) = 6 m s⁻¹. (iv) v = (4 − 0) ÷ (2 − 0) = 2 m s⁻¹. (v) Distance = 4 + 6 + 10 = 20 m; displacement = 0 m (the car is back at the start). 1 f . 1 f .

• Approach: the slope of a displacement-time graph is the velocity; a flat line means no movement.

• (i) Speed has size only, so it is a scalar. 2 marks. (ii) In B the displacement stays at 4 m, so the car is not moving. 2 marks.

• (iii) The steepest slope is in C. Velocity = change in displacement ÷ time = (10 − 4) ÷ (5 − 4) = 6 m s⁻¹. 2 marks. (iv) In A: (4 − 0) ÷ (2 − 0) = 2 m s⁻¹. 2 marks.

• (v) Distance moved: A 4 m, C 6 m, D 10 m (back from 10 m to 0), total 20 m. At 8 s the displacement is 0 − 0 = 0 m. 2 marks.

(c) A student connects two resistors in series with a 12 V battery. (i) Calculate the total resistance of the circuit. (ii) Calculate the current in the circuit. (iii) Calculate the potential difference across the 6 Ω resistor. (iv) Name the instrument used to measure current and state how it is connected in a circuit. 6 Ω 3 Ω 12 V Circuit diagram (not to scale).

(c) Answer: (i) R = 6 + 3 = 9 Ω. (ii) I = V ÷ R = 12 ÷ 9 = 1.33 A. (iii) V = IR = 1.33 × 6 = 8.0 V. (iv) An ammeter, connected in series.

• Approach: in series the resistances add; the same current flows through each part; V = IR.