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2020 WAEC Physics Questions and Answers
WAEC August 27, 2020 • 5 months ago • 4 Comments

## WELCOME TO EXAMRELEIF 2020 WAEC ANSWERS PAGE

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# 👑 2020 WAEC PHYSICS ANSWERS👑

1-10: DCCAACDCCC
11-20: BDBABBDCCB
31-40: BDDDDACCCA
41-50: AAAABBCBBC

(1)
Original length Lo = 3m
extension e = 3Lo = 3×3 = 9m
F ∝e
F = ke where k = 982.3Nm‐²
F = 982.3×9 = 8840.7N
The force that produces the extension F = 8840.7N

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(2a)
Flat metal plate are mainly used to collect heat for space heating in solar panels for heat transfer.

(2b)
Thermal insulator is used for reduction of heat transfer between objects in thermal contact

(2c)
tubes is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
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(3a)
Plastic

(3b)
The refractive index of the core must be greater than that of the cladding.
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( 4)
V ∝ T^x U^y
LT‐¹ ∝(MLT^‐²)^x(ML^‐1)^y
LT‐¹ ∝ M^xL^xT^‐²x × M^yL^-y
LT‐¹ ∝ M^(x+y) L^(x-y) T^‐²x
Comparing
X-y = 1 —–(1)
X+y = 0 —–(2)
-2x = -1 —-(3)
From equation 3,
X = 1/2
Putting X = 1/2 into eqn 2
y = -1/2
Equation is:
V ∝ T½ U‐½
V = √T/U
V = K√T/U
Where k is constant

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SECTION B
(5)
Escape velocity = VE
Radius of the earth = R
Acceleration due to gravity = 10ms²
Escape velocity Be=√2R
VE=√2*10R
VE=√20R

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(6)
θ = 30°, g = 10m/s²
Time of flight, T = 25seconds
Using,
Time of flight, T = 2usinθ/g
25 = 2usin30°/10
2u(0.5) = 250
u = 250
Velocity of projection, u = 250m/s

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(8ai)
A torque is defined as a measure of the force that can cause an object to rotate about an axis

(8aii)
Factors that determine torque are;
– The magnitude of the force
– The angle between the force and the lever arm

(8bi)
Free fall simply means the act of which are objects fall freely under the influence of gravitational force. An object under free fall does not encounter air resistance

(8bii)
Height of tower H = 40.0m
Velocity v = 10.0m/s, time t= ? , g=10.0m/s

Using the relation
S= ut + 1/2gt^2
H= ut + 1/2gt^2
40= 10t + 1/2*10t^2
4= t + t^2/2
= t^2 + 2t – 8=0 ( solving quadratically)
= (t+4)(t-2)=0
t+4=0 or t-2=0
t= -4 or t=2

Therefore time to fall on the ground t=2s

(8c)
Side of cube of wood = 8.0cm
2.0cm = 1/4 of the side immersed in water
R.density of water Rw = 1.00
R.density of Oil = Ro = 0.72
Volume of the wood V = L³
= 8×8×8
V = 512cm³
Volume immersed in water = 1/4×512 = 128cm³
Weight of water displaced = 128g × Rwater = 128×l
By applying the principle of flotation
Mass of wood = 128×Rw
=128 × l = 128g

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(10ai)
Critical angle is defined as the angle of incidence in the denser medium when the angle of refraction in the dense medium is 90°

(10aii)
The conditions necessary for total internal reflection to occur
1. Light must be traveling from an optically more dense to an optically less dense medium.
2. The angle of incidence in the denser medium must be greater than the critical angle.

(10aiii)
Three practical applications of total internal reflection:

(i) Mirages
(ii) Field of view of a fish under water.
(iii) Refractometer.
(iv) Optical fibre.
(v) Binoculars.

(10b)
Two effects of refraction:
(i) Apparent depth of a swimming pool.
(ii) Apparent bending of a stick partly immersed in water.

(10ci)
Progressive wave is defined as a wave that transfers energy in traveling or moving away from the source of the disturbance.

(10cii)
y = 0.5sin(1000πt – 100πx)/17 = y = Asin(2πx/λ – wt)

(∝) at = 1000πt
===》 w = 1000
But w = 2πf
2πf = 1000π
f = 1000/2
f = 500Hz

(β) 2πx/λ = 100π/17 x
2/λ = 100/17
λ = 2×17/100
=0.34m

(γ) V = fλ
= 500 × 0.34
=170m/s

=====COMPLETED=====

BEST OF LUCK

Anonymous Aug 28, 2020 • 11:32 AM •

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Anonymous Aug 28, 2020 • 1:25 PM •

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Gentility Aug 28, 2020 • 1:27 PM •