## Physics 2020 Past Question | WAEC

46. Which of the following units is not fundamental?

**A.**Metre**B.**Kilogram**C.**Joule**D.**Candela

**47. **The vacuum between the double walls of a thermos flask reduces heat loss through

**A.**conduction and radiation**B.**convection and conduction**C.**radiation only**D.**conduction only

**48. **In photoelectric effect, the number of electrode emitted per second from a metallic surface is proportional to the

**A.**intensity of the incident radiation**B.**frequency of the incident radiation**C.**energy of the incident radiation**D.**work function of the metal.

**49. **When two cells of negligible internal resistances and equal e.m.f. denoted by E1and E2are connected in parallel, combined e.m.f. E is given by

**A.**E = E1 + E2**A.**E = E1/E2**B.**1/E=1/E1+1/E2**C.**E = E1 = E2

**50. **Which of the following statement about viscosity is not true? it

**A.**depends on areas of the surfaces in contact**B.**occurs in fluids**C.**is independent of the relative velocity of the layers**D.**depends on the tangential force between the layers

### PHYSICS THEORY PAST QUESTIONS 2020 WITH SOLUTION

- An elastic material of length 3m is to be stretched to reduce an extension three times its original length. Calculate the force required to produce the extension

**2. **In a solar panel for heat supply, state the function of each of the following parts: (a) metal flat plate; (b) thermal insulator: (c) tubes.

**3. **(a) In the design of an optical fibre, what type of material is most suitable for the design of the core?

(b) State one condition necessary to confine signals to the core of an optical fibre.

**4. **The velocity v, of a wave in a stretched string, depends on the tension T, in the spring and the mass per unit length of the spring. Obtain an expression for v in terms of T and u, using the method of dimensions.

**5. **A satellite launched with velocity VEEjust escapes the earth’s gravitational attraction. Given that the radius of the earth is R, show that VE= √20R [g = 10ms^{−2}

**6. **A bullet is fired from a gun at 30oto the horizontal. The bullet remains in flight for 25s before touching the ground. Calculating the velocity of projection. [g = 10ms^{−2}]

**7. **State three properties of lasers that make them preferable to ordinary light beam**.**

**8. **(a)i) Define a torque.

(ii)State three factors that determine a torque

(b)(i) Define free fall.

(ii) A body is thrown vertically upwards from the top of a tower 40.0m high with a velocity of 10.0ms^{−1}. Calculate the time taken for the body to reach the ground. [g.= 10.0ms^{−2}]

- c) A cube of wood of side 8.0cm, floats at the interface between oil and water with 2.0cm of its surface below the interface as shown in the diagram below. Given that the relative densities of oil and water are 0.72 and 1.00 respectively, calculate the mass of the wood

**9. **(a)Explain resonance frequency as applied in RLC series Circuit.

(ii) Sketch a diagram to illustrate the variation of frequency, f, with the resistance, R, the capacitive reactance, Xc and the inductive reactance XLL, in RLC series circuit.

(iii) Using the diagram drawn in (a)(ii) state whether the current in the circuit leads, lags or is in phase with the supply voltage when: (α) f = foo; (β) f < foo ; γfoo; when foo is the resonant frequency.

b)(i) Define mutual inductance.

(i) The coil of an electric generator has 500 turns and 8.0cm diameter. If it rotates in a magnetic field of density 0.25T, calculate the angular speed when its peak voltage is 480V. [π = 3.142].

**10. **

- a) (i) Define Optical angle.

(ii) Explain two conditions necessary for total internal reflection to occur.

(iii) List three practical applications of total internal reflection.

(b) State two effects of refraction.

(c)(i) Define progressive waves.

(ii) A plane progressive wave is represented by the equation y = 0.5 sin(1000πr = 100πλ/17) where y is in millimetres, t in seconds and x in metres. Calculate the: (α) frequency of the wave; (β)of the wave; (γ) speed of the wave