# WAEC Physics Questions & Answers 2021 0
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## WAEC Physics Answers & Questions 2021

No (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.

(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.

No (7)
(i)Coherence
(ii)Directionality
(iii)Monochromatic

No (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
No (5)
Escape velocity = VE
Radius of the earth = R
Acceleration due to gravity = 10ms²
Escape velocity Be=√2R
VE=√2*10R
VE=√20R
No (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

(8ai)
A torque is defined as a measure of the force that can cause an object to rotate about an axis
WAEC Physics Questions 2021 and Answers
(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

L
(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

1)
Velocity of projection U_p =10m/s
T= sqr root 2h/g Where H=1
G=10
T=sqr root 2*1/10
=sqr root 0.2
=0.447s
V=UsinTita + gt V=10sin90 + 10*0.447
V=10 +4.45
V=14.5m/s
=================

(2)
(i) The position of the ion of the atm of the element in the
electrochemical(activity)series.
(ii) the nature of the electrode.
(iii) the concentration of the electrolyte
====================================
3)
l=6.5m
d=3.0mm=0.003m
e=0.20mm=0.0002m
F=60N
stress=F/A
A=pie*D^2/4
=3.142*0.003^2/4
=3.142*9*10^-6/4
=7.065*10^-6/4m^2
stress=60/7.065*10^-6
=8.49*N/m^2
(7)
Doping of semiconductor increases the number of holes and electrons in
the semiconductor, thereby making it impure which makes it to be useful
or active.

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