Here is the waec GCE PHYSICS answers for 2021,

Physics OBJ

11-20: CBDBBCDBCA

21-30: CCAABBBDBC

31-40: ACDDCBAABA

41-50:

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1a) Power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one joule per second. In older works, power is sometimes called activity. Power is a scalar quantity.

(1a)

Power; = f*d/t = MLT^-² * L/T =ML²T^-³

(1b)

Force; = m*a =MLT^-²

(1c)

Pressure; F/A = MLT^-²/L² =ML^¹T^²

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(2)

(i)Boron

(ii)Aluminium

(iii)Gallium

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(3a)

(i)Iron

(ii)nickel

(3b)

(i)Magnets are used in magnetic compass, doorbells, refrigerators.

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(4)

w = 2π/T

V/R = 2π/T

R/V = T/2π

R = VT/2π

= 8×10³×5×10³/2×3.14

= 6.37×10⁶m

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(5)

Given :

e= 5.00×10-³m

P.E= 50J

Using; P.E = 1/2ke²

50 = 1/2×k×(5×10-³)²

k = 50×2/(5×10-³)²

= 50×2/25×10-⁶

k = 4×10⁶N/m

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O(11ai)

(i)Lines of force Start only on positive charges and end only on negative charges.

(ii)Lines of force do not cross each other

(11aii)

[img]https://i.imgur.com/jOlDgxo.jpg[/img]

(11bi)

The surface density of a conductor is the quantity of say electric charge per unit area flowing through it.

(11bii)

The opposition to the flow of alternating current altered by a capacitor is known as capacitive reaction ie Xc

(11ci)

From ; Xc =1/2πfc, when frequency is increased, Xc drops. Consequently, from I = v/Xc, current increases

(11cii)

Vt = VmSin (wt-90°)

If It = Im Sin wt

Voltage lags by 90°

(11ciii)

Xc = 1/2πfc

:. C = 1/2πfXc = 1/2*3.14*100*500

= 1/314000

= 3.185µF

(11d)

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