Waec

2018 Waec Physics Answers (May/June Expo)

2018 waec agricultural science theory & obj answers

2018 WAEC PHYSICS ANSWERS

*PHYSICS OBJ*

1-10 CAABACBADB
11-20 ACCCDABDCC
21-30 DBADCABCAB
31-40 CCBBCCBABD
41-50 BDCDBABBDC

 

1a)
Strain is force (a part of one’s body or oneself) to make an unusually great effort.

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(2)
Material used for making optical fibers
(i) Silicon Dioxide
(ii) Silica Powder
(iii) Germanium Tetrachloride

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3)
-Diamagnetic material
-Paramagnetic material
-Ferromagnetic material

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(4a)
An intrinsic semiconductor is an undoped semiconductor that is a pure semiconductor without any significant dopant
species present.

(4b)
The P Type semiconductor is a type of semiconductor that carries a positive charge, while the N type semiconductor carries a negative charge.

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5)
Range = u²Sin2tita/g
At maximum range
Sin2tita = 1
2tita =sin^-1(1)
2tita = 90dgrees
Tita = 90/2 = 45degree

Maximum height reached = u²sin²tita/2g
=u²(sin45)²/2g
=200²(sin45)²/2(10)
=40000(1/√2)2/20
=40000(1/2)/20
=20000/20
=1000metres.

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7
(a). LASER stands for Light Amplification by Stimulated Emission of Radiation.

(b). A laser is a device that emits a beam of coherent light through an optical amplification process.

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8)

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10a) Diffraction refers to various phenomena that occur when a wave encounters an obstacle or a slit. It is defined as the bending of light around the corners of an obstacle or aperture into the region of geometrical shadow of the obstacle.

10b)
Critical angle: the angle of incidence beyond which rays of light passing through a denser medium to the surface of a less dense medium are no longer refracted but totally reflected.

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(12a) This is defined as the amount of energy that must be supplied to a nucleus to completely separate it’s nuclear particles (nucleons)

(12b)
(i) They have short wavelength and high frequency.
(ii) They are highly penetrating.
(iii) They travel in straight lines.
(iv) They don’t require material medium for their propagation.

(12c)
-It is used in production of electricity.
-It is used to study and detect charges in genetic engineering.
-It is used in agriculture.
-It is used in treatment of cancer.

(12di)
E = hf-hfo
but f = v/landa
E= v/landa.h – wo
Where wo = hfo = work function
f= frequency
landa = wavelength
Hence
hf = hfo – E
f = hfo – E/h
f = wo – E/h
Recall; that v = f landa
Therefore f = v/landa = 3×10^8/4.5×10-7
=3/4.5 × 10^8+7
=6.6×10^14Hz
f = 6.6×10^14Hz

(12dii)
E = hf
=6.6×10^-34 × 6.6×10^14Hz
=43.56×10^-20J

(12diii)
Energy of the photoelectron E = hf – vo
=Energy of incident electron – work function
=4.356×10^-19J – 3.0×10^-19J
=1.356×10^-19J

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