# WAEC Physics Obj & Theory Questions & Answers – 2020 May/June Exam

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`WAEC Physics Essay & Obj Answers - 2020 May/JuneExam`

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KEEP REFRESHING…..
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✨ PHYSICS OBJ

*Use this*👇🏽🇳🇬

PHYSICS OBJ
1-10: DCCAACDCCC
11-20: BDBABBDCCB
31-40: BDDBDACCCA
41-50: CAAABBCBBC

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SECTION A

(1)
L2=3l (3 * original length l1)
L1=3m
L2=3 * 3
=9m
F=?
K= 982.3 N/m
f=ke
f=982.3 * 3
f=2946.9N

f1/e1=f2/e2
2946.9/3=f2/9
f2=8840.7N
≈8.841 * 10³N

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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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SECTION B

(6)
[check image]

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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

(9)
[Check image]

9ci) Eddy current loss is conductive power loss produced by circulating currents induced in response to AC flux linkage, flowing against the internal resistance of the core.
Eddy currents (also called Foucault’s currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday’s law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field.
In order to reduce the eddy current loss, the resistance of the core should be increased by laminating the core.

9cii) i) eddy currents are utilized in energy meters and automobile speedometers

ii) Used in induction alternating current (AC) motors

iii) Used in free-fall devices

iv) Used as a way of detecting coins in vending machines,

V) Used to increase temperatures uniformly in induction furnaces, and in proximity/displacement

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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)
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

2a) A Flat Plate Collector is a heat exchanger that converts the radiant solar energy from the sun into heat energy using the well known greenhouse effect. It collects, or captures, solar energy and uses that energy to heat water in the home for bathing, washing and heating, and can even be used to heat outdoor swimming pools and hot tubs.

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.

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

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