# 2020 WAEC PHYSICS OBJ AND THEORY ANSWERS

2020 WAEC PHYSICS OBJ AND THEORY ANSWERS

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**OBJECTIVE ANSWERS:**

**Friday, 28th August 2020**

**Physics-Obj**

**Physics-Obj**

**1DCCAACBCCC**

**11BDBABBACAC**

**21BCBACBBACA**

**31BDDDDACCCA**

**41AAAABBCBBC**

**THEO**

**THEORY/ESSAY ANSWERS:**

**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…**

**=======================================**

**(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.**

**=====================================**

**(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**

**===============================**

(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.

===============================

(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.

===============================

(7)

(i)Coherence

(ii)Directionality

(iii)Monochromatic

=============================

(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

**=============================**

**(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**

**=================================**

**(5)**

**Escape velocity = VE**

**Radius of the earth = R**

**Acceleration due to gravity = 10ms²**

**Escape velocity Be=√2R**

**VE=√2*10R**

**VE=√20R**

**=============================**

**(4)**

**(5)**

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