WAEC 2021 Physics Answer – May/June Expo

WAEC Physics Answer

The West African Examinations Council WAEC Physics Questions Answers 2021 Objective and Theory Update.

PHYSICS OBJ:
1-10: AAABACCDDB
11-20: ACCDCBCBAC
21-30: CCCBBDDBBB
31-40: ACBBCCCAAD
41-50: ABADCCBAAC


(1&2)

(1)
Workdone = 1/2Fe
= 1/2 × 40 × 1/100
= 1/5 = 0.2J


(2a)
(i)Navigation satellites e.g global position system – GPS
(ii) Communication satellites eg ANIK

(2b)
V = 2πR/T
For every second,
Speed, V = 2πR
V = 2 × 22/7 × 6300
V = 39,600km/s


 

(3&4)

 


(6)
(i) Reflection
(ii) Refraction
(iii) Diffraction


(7a)
The scientific principle underlying the operation of a fibre optics is the principle of total internal reflection by which light signals can be transmitted from one place to another with a negligible loss of energy.

(7bi)
Core: The core is the light transmission area of the fibre, either glass or plastic cladding. The function of the cladding is to provide a lower refractive index at the core interface in order to cause reflection within the core so as to enable light waves transmitted through the fibre.

(7bii)
Cladding: It functions as a gadget that provides a clear refractive index at the core interface in order to cause reflection within the core so that light waves are transmitted through the fibre.


 

(8)

 

(8ai)
Hooke’s law states that the extension e produced by an elastic material is directly proportional to the applied force provided the elastic unit is not exceeded.

(8aii)
(i) Given extension, e = I2 – I1 = 0.75 – 0.20 = 0.55m
Force applied, Fe = (1.95 – 0.30) × 10
= 1.65 × 10 = 16.5N
Force constant , K = F/R = 16.5/0.55 = 30N/m

(ii) Using F = K (I1 – Io)
m1g = K ( I1 – Io)
= 0.30 × 10 = 30(0.20 – Io)
= 0.10 = 0.20 – Io
Io = 0.20 – 0.10
Io = 0.10m
Length of spring when it was unloaded = 0.10m

(8bi)
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration.

(8bii)
(i) Temperature
(ii) Size of particles

(8biii)
Rate of diffusion is inversely proportional to the square root of density under given conditions of temperature and pressure. ie R ∝ 1/√d

(8c)
T = circumference of the orbit/orbit velocity
T = 2πR/v
But V = √GM/R
T = 2π√R³/GM


(9)

 


(11)

 

(11ai)
Root measurement value of an alternating current is the value of A.C current that has the same heating affect as a D.C current

(11aii)
Impedance is the affective resistance of an electric circuit arising from the combined affects of ohmic resistance and reactance. (i.e resistors, indicators and capacitors)

(11b)
Current in circuit , I = 60/120 = 0.5A
Voltage across device , Vr = 120V
Voltage across capacitor , Vc = √V² – Vr
Vc = √240² – 120²
Vc = 207.846V
Ic = I = 0.5
Xc = Vc/Ic = 207.846/0.5 = 415.7Ω
Capacitance, C = Xc/2πf = 415.7/23.14250 = 1.323F

(11ci)
The capacitance of a capacitor is the ratio of the amount of charge on its plates to the potential difference between them. ie C = ∑/V

(11cii)
(i) Charge in both capacitors are the same
∑1 = Q2
ie C1V1 = C2V2 ………(1)
Total capacitance ,C = C1C2/C1+C2
C = C2/1+C2/C1 = C2/1+V/V2
C = C2V2/V1+V2 = C2V2/2
C= 1/2C2V2

(ii)Voltage across, V1 = (C2/C1+C2) × V
V1 = (C1/C1+C2) × V
But C1/C2 = d2/d1 = 5/2
V1 = (1/(5/2+1)) × 2 = 2/7 ×2 = 4/7Volts.

 

GOODLUCK!!!

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