# 2020 WAEC PHYSICS OBJ AND ESSAY QUESTIONS/ANSWERS VERIFIED EXPO

**Physics-Obj
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completed

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Theory-Answers.

(12)

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(9a&b)

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Use this number 10.

(10)

(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:

[Choose three]

(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

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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 radius

– 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)

R.d of oil =R1 = 0.72

R.d of water = R2=1.00

R.d of liquid= R1/R2= 0.72/1 = 0.72

R.d = density of wood(P1)/density of water(P2)

0.72=P1/1.00

P1= 0.72*1.00=0.72g/cm³

But density of wood= mass of wood/volume of wood

0.72= mass of wood/8*8*8

Mass of wood = 0.72*512 = 368.64g

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(4)

V∝ Tx μy

LT-∝(MLT-²)x(MLT-¹)y

LT-¹∝ m*L*T-²x x m y L-y

LT-¹∝ m(x+y)L(x-y)T-²x

Comparing

X-y=1

X+y=0

-2x=1

From equation 3

X=½

Putting x = ½ into (eq) 2

y=-½

Equation is

V∝ T½ μ-½

V∝ √T/μ

V= k√T/μ

Where k is constant

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(6)

Angle at horizontal θ = 30°

Time of light , T = 25sec

Velocity of projection u = ?

But T=2using sinθ/g

25= 2u*sin30/10

25=0.5u/5

0.5u=125

U=125/0.5

=250ms-¹

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(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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(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)

highly purified silica glass.

(3b)

To confine the optical signal in the core the refractive index of the core must be greater than that of the cladding.

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(7)

(i)Coherence

(ii)Directionality

(iii)Monochromatic

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(1)

Original length Lo= 3m

Extension e = 310 = 3*3= 9m

F×e

F=ke where k = 982.3NM-²

F=982.3*9=8,840.7N

The five that produce the extension F = 8.840.7N

Categories: WAEC

Emma mecha

by nice on Aug 28, 2020