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NABTEB 2017 Physics Essay And Objectives Posted Answers

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Physics-Theory-Answers

1a)
S/N| Quantities| Formula| unit| dimension
1| force| f=ma| newton(N)| kgms^-2 or MLT^-2
2| momentum(p)| p=mv| kgms^-1 or MLT^-1
3| density| e=m/v| kgm^-3 or ML^-3

1bi) Relative density of a substance: This is the density of a substance to the density of water i.e.
Relative density = Density of substance / Density of water

1bii) Title of experiment: Determination of density of extracted stone from a rock

Apparatus - Eureka can, thread, stone, measuring cylinder, wooden stand 

Reagent - Water

Procedure:-
-A hard stone is extracted from a rock
-weigh the obtained stone
-thigh a thread round stone
-the mass of a stone is obtained using a lever balance
-the stone with thread is place in water is displaced and the volume of the displaced water is equivalent to the volume of the solid guage by measuring cylinder placed beside the eureka can the volume of water dropped into it
-has the mass and volume has been obtained the density can be determined as :-

Density:-mass of irregular object(stone)/volume of water displaced 

1c)
data given
F=60N, e=0.3mm =0.3*10^-3m
length=2m, d=1.5mm=1.5*10^-3m

1ci)
stress=force/area
area=^d^2/4=3.142*(1.5*10^-3)^2/4
A=1.767*10^-6m^2
stress=60/1.767*10^-6=33.95*10^6N/M^2

1cii)
strain=extention/original length
=0.3*10^-3/2 =0.15*10^-3
strain=0.15*10^-3

1ciii)
young modulus=stress/starin
=33.95*10^6/0.15*10^-3
=226.33*10^9N/M^2

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2ai)
i)change of state of body
ii)thermionic emssion
iii)increase in temperature
iv)photoelectric emission

2aii)
i)thermal expansion
ii)thermal conductivity
iii)change in resistance
iv)capillarity

2bi)
i)increase in pressure leads to increase in boiling point
ii)addition of common salt on the boiling point of water decreases it

2bii)
tabulate
-saturated vapour-
i)it does not obey charles law
ii)it does not obey boyles law
iii)it increase as temperature increases
-unsaturated vapour-
i)it obey charles law
ii)it obey boys law
iii)it does not

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3ai)
drawing
Negative charge

3aii)
drawing

3bi)
eletric field potential this is the work done in taking a unit positive charge from infinty to the point in questing i.e V=Q/4pie E.R

3bii)
eletric field intensity this is the ratio of electric force to the test charge
E=Fe/q (N/C)

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4ai)
mechanical wave is a wave that is an oscillation of matter, and therefore transfers energy through a medium.

4aii)
electromagnetic wave is a wave produced by the acceleration of an electric charge and propagated by the periodic variation of intensities of, usually, perpendicular electric and magnetic fields.

4b)
Data given, 
Period T=2.5 ×10^-6s
λ=3×10^8 m/s
λ=VT =3×10^8 × 2.5 ×10^-6
=7.5×10^2m
Wavelength =7.5×10^2m
=750m

4ci)
i)light must be travelling from the dense to less dense medium 
4cii) the angle of incidence in the denser medium must be greater than critical angle

4ciii)
i)THE mirage
ii) Field of view of a fish under water

4d)
given that
y=2sin(0.5x-500t)
y=2sim(0.5x-500t)
by comparing with
y=Asin (t+-kn)
w=500rad/s, k=0.5

4di)
K=2^/r
r=2^/k=2^/0.5^=4m
wave length =4m

4dii)
W=2^/T
T=2^/T=2^/500^=4*10^-3 5
speed (v) =r/t
=4/4*10^-3=10^3m/s
v=1000m/s

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5ai)
light

5aii)
frequency

5bi)
Tabulate
-Photo emission-
i)it occurs at fixed temperature and pressure 
-evaporation-
i)it occurs at all temperature

5bii)
i)photometer
ii)television camera
iii)burglars alarms
iv)automatic doors

5ci)
Data given, 
W=2.0eV
λ=4.5×10^-9m
C=3.5×10^8m/s
h=6.6×10^-35js
W=hfo
Fo = w/h
2×1.6×10^-19/6.6×10^-35
=0.4848×10^15Hz
Fo=4.848×10^14Hz
Threshold frequency =4.848×10^14Hz

5cii)
Maximum energy of photo electron
E=hf - W
=hc/λ - w
=6.6×10^-34 ×3 ×10^8/4.5×10^-7
=4.4×10^-19 - 3.2×10^-19
=1.2×10^-19

5d)
i) Each spectral is caused by an electron
ii)Electron can exist only in circular orbits of definite quantum
energy
Limitation:
i)the electron is restricted to certain energy level 
ii) The orbital is identified by a set of three quantum numbers

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