**WAEC PHYSICS 2020 SOLUTIONS**

OBJ PHYSICS

01-10: DCCAACDCCC

11-20: BBBA••••••

15.C 16.D 18.C

21-30:* ••••••••••

*31-40:* ••••••••••

Part ii a) DescriptionTorque is the rotational equivalent of linear force. It is also referred to as the moment, moment of force, rotational force or turning effect, depending on the field of study. The concept originated with the studies by Archimedes of the usage of levers.

Part ii b) A free falling object is an object that is falling under the sole influence of gravity. Any object that is being acted upon only by the force of gravity is said to be in a state of free fall. … Free-falling objects do not encounter air resistance.

(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

(3a)

Material made from silica

(3b)

To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The boundary between the core and cladding may either be abrupt, in step-index fiber, or gradual, in graded-index fiber. Light can be fed into optical fibers using lasers or LEDs.

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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

(2a)

A typical flat-plate collector is a metal box with a glass or plastic cover (called glazing) on top and a dark-colored absorber plate on the bottom. Sunlight passes through the glazing and strikes the absorber plate, which heats up, changing solar energy into heat energy.

(2b)

Insulation in thermal solar collectors prevents loss of accumulated heat in the solar collector and improves absorption efficiency.

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(7)

(i)Coherence

(ii)Directionality

(iii)Monochromatic

8ai) Torque is the rotational equivalent of linear force. It is also referred to as the moment, moment of force, rotational force or turning effect, depending on the field of study

8aii.)

1. the strength of the magnetic field of the stator

2. the strength of the magnetic field of the rotor

3. the phase angle difference between the magnetic fields of stator and rotor

(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…

(8bi)

In Newtonian physics, free fall is any motion of a body where gravity is the only force acting upon it.

(8bii)

S=ut+½gt²

40=½10t²

40×2=10t²

t=√8

t=2.8sec

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(10ai) Critical angle, in optics, the greatest angle at which a ray of light, travelling in one transparent medium, can strike the boundary between that medium and a second of lower refractive index without being totally reflected within the first medium.

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