2020/2021 WAEC/NECO Answers: 2021 Waec Gce Physics answers.

(12a)
(i) Cosmic rays
(ii) Rocks and soils

(12b)
Because the mass of a radioactive isotope decreases exponentially. Also, the source and intensity of radiation differs.

(12c)
(i) Dielectric materials
(ii) 


(12d)
(i) Alpha radiation
(ii) Beta radiation

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(6a)
(i) It can cause short and long term sun burn effects. 
(ii)It can cause blindness when flashed to the eyes.

(6b) Energy = hf
= 6.60×10^-34 × 4.82×10^14
= 3.18×10^-19J
= 1.99ev

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(7) 
V = 2Ï€R/T
R = 9.6×10^6 + 6.4×10^6 =16×10^6 m
T = 24hrs =(24×60×60)s 
V = 2×3.142×16×10^6/24×60×60
V = 1162.96m/s

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(11a) 
Lenz's law states that an induced current is in such direction that it's magnetic effect opposes the change by which the current is induced. 

(11b)
(i) Magnets are used in construction of speakers. 
(ii) They are used to store data in computers. 
(iii) Used in magnetic resonance imaging machines. 

(11ci)
(a) Two coils: So as to produce an induced current from one coil to the other. 

(b) an iron core: To increase the strength of the magnetic field.

(11cii)

(11d)
Total resistance in series 
Rt = R1 + R2
= 500 + 400
Rt = 900ohms

Taking E = 6v
E = V + ir 
E = VR + Ir 
E = I ( R + r) 
I = E/R + r
taking r = 200ohms
I = 6/900+200
I = 6/1100
I = 0.005A

Hence the voltmeter reading 
V = IR
= 0.005 × 200
= 1.09v

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(1a)
Young modulus of a material or the modulus of elasticity. 

(1b)
Potential Energy to kinetic Energy.

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(2)
e = 0.7m
m=60 × 10-³kg = 6.0×10-²kg
K = 200Nm-¹
W = 1/2ke² = 1/2mv²
1/2ke² = 1/2mv²
V² = ke²/m = 200×0.7²/6.0×10-²
V² = 98×10²/6
V² = 16.33×10²
V = √1633
V = 40.4
Speed = 40.4ms-¹

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(3)
(i) Optical fibres have extremely high bandwidth
(ii) They have longer transmission distance
(iii) They have resistance to electromagnetic interference


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(4a)
It is used in geometric stations used to move a satellite from low earth orbit into a geostationary orbit. 

(4b) 
Polar orbit satellite is used in earth mapping.

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(5a)
(i) Centripetal force
(ii) Centrifugal force

(5b)
Ft = mDv
where F = force
t = time
Dv = change in velocity
m = mass of object

Hence F = mDv/t

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