2020 WAEC PHYSICS OBJ AND THEORY ANSWERS

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Friday, 28th August 2020

Physics-Obj

Physics-Obj

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PLEASE NOTE: asteric(*) MEANS multiplication(x).

(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)

Coming…

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(10ai)

Critical angle: this is the angle of incidence that

provides an angle of refraction of 90-degrees.

(10aii)

(i) Light must travel from a denser medium to a rarer medium and

(ii) the angle of incidence inside the denser medium must be greater than the critical angle.

(10aiii)

-In elescopes application

-In microscopes applications

-In the binoculars

(10b)

(i)Bending of light;If light is moving from rarer to denser medium then it moves towards the normal.

If it is moving from denser to rarer medium then it moves away from the normal.

(ii)Change in wavelength of light

(10ci)

(i)myopia

(ii)Long sightedness

(ii)short sightedness

(10cii)

(i)concave lens

(ii)Convex lens

(iii)Contact lenses

(10di)

convex mirror has a wider field of view

(10dii)

The disadvantages of convex mirror are that they make it appear like those objects are at a more noteworthy distance than they actually are.

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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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(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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(2a)

Metal flat plate: It is a collector of heat that converts the radiant solar energy from the sun into heat energy by the process of greenhouse effect.

(2b)

Thermal Insulator: It prevents loss of accumulated heat in the solar collector and thereby improves its absorption efficiency.

(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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(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

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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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(4)

(5)

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