WAEC GCE 2019 - PHYSICS ANSWER

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ANSWERS:

(2a)
H=ut+½gt²
Where H=80m, t=?
80=0(t) + ½(10)(t²)
80=0 + 5t²
80=5t²
80/5=t²
16=t²
t=√16
t=4s

(2b)
Range = U²/g
20²/10
=400/10
=40m



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(3)
F = KAV/L
FL = KAV
K = FL/AV
Where F = ma
= MLT-²
r = M, V = LT-¹
And A = M²

K = MLT-² × M/m² × LT-¹
K = LT-² ×L-¹T-¹
K = T-¹



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(5)
(i) Temperature of the body
(ii) Nature of the body
(iii) Distance between the body and the radioactive source

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(6a)
Ferromagnetic materials are those substances which exhibit strong magnetism in the same direction of the field, when a magnetic field is applied to it.

(6b)
(i) Iron
(ii) Nickel

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(8)


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(11a)
An electric field is a region where an electric force is experienced by a charged body.

(11b)
In a tabular form
Under gravitational potential
(i) Scalar quantity
(ii) Unit is Joule per coulomb

Under gravitational field strength
(i) Vector quantity.
(ii) Unit is Newton per coulomb.

(11ci)
Equivalent capacitance = 5uf//(2uf + 2uf)
= 5uf // 4uf
= 5×4/5+4 uf
= 20/9 uf
= 2.22uf

(11cii)
Total energy stored = 1/2cv²
= 1/2×20/9×10^-6×12×12
=160×10^-6
= 0.00016Joules.

(11di)
Given: Im = 20×10^-3A; V = 25sin100πl
Capacitive reactance Xl = Vm/Im = 25/26×10^-3 = 1250ohms

(11dii)
1/2Ï€fc = Xl
Where f = 50Hz
1/2×22/7×50c = 1250
314.286c × 1250 = 1
392857 c = 1
C = 1/392857 = 2.545×10^-6F
= 2.545uf

(11e)
A phasor diagram is a graphical way of representing the magnitude and directional relationship between two or more alternating quantities.
name



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(12a)
Thermoelectrons are electrons emitted at a high temperature such as one produced in a thermionic valve. They are negatively charged.

(12b)
(i) Low voltage battery
Used to heat the heater or heating element.
(ii) Target metal
Used to collect the emitted electrons.

(12Ci)
α - particles has a helium nuclei He while a β-particle has high energy electrons.

(12Cii)
α - particle has a charge of +2e while β-particle has a charge of -e.

(12di)
The radioactive decay law states that the probability per time that a nucleus will decay is constant, independent of time.

(12dii)
(i) Damage to skin.
(ii) Causes cancer.

(12ei)
Given 238 U --> m X + 2α
92 n
= 238 U --> m X + 2 4He
92 n 2
m+(2×4) = 238
m + 8 = 238
m = 238 - 8 = 230
Also
N + (2×2) = 92
N + 4 = 92
N = 92 - 4
n = 88

(12eii)
230
X
88

No of neutrons = 230 - 88 = 142
Neutron - Proton ratio = 142/88 = 1.61

(12eiii)
It is unstable.








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