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# NABTEB 2017 Physics OBJ And Theory Expo Answer

NABTEB Physics Obj And Theory/Essay Questions and Answer – May/June 2017 Expo Runz

Physics-Obj

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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)
3biii)
electric field intensity
E=Fe/q = Q/4^E.r^2
electric potential at the surface of the sphere
V=Q/4^E.r
3c)
data given
r=5.0*10^-3m , V=5.0*10^4
3ci)
electric field intensity
E=v/r=5.0*10^4/5.0*10^-3
E=1*10^7 N/C
3cii)
force on the electron
E=Fe/q
Fe=Eq=1*10^7*4^E.rv
=10^7*0.111*10^-9*5*10^-3*5*10^4
=2.75*10^-1 =0.275N
—————–
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
-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
————————–
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)Automatic doors
iv)burglars alarms
(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
—————-
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
ii) the angle of incidence in the denser medium must be greater than critical angle
4cii)
i)THE mirage
ii) Field of view of a fish under water
——————–
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 t
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