NABTEB 2018 Physics Answer Obj and Essay– May/June Expo

Verified NABTEB 2018 Physics ANSWER

PHYSICS OBJ.
1-10DCDBCBAAAB
11-20BBCACDBACD
21-30DABBCBBDAA
31-40DAADDCCBBC
41-50CCBDAACCCB

PHYSICS THEORY
(1a)
The moment of force about a point it is the product of the force and the perpendicular distance of its line of action from the point

(1aii)
The principle of moments states that if a body is in equilibrium, the sum of the clockwise moments about any point on the body is equal to the sum of the anticlockwise moments about the same point.

(1b)
DRAW THE DIAGRAM
Anticlockwise moment = clockwise moment
60g x 15 = M x 15
M = 60g x 15/15
M = 60g
Mass of meter rule = 60g

(1ci)
The moment of a couple is the product of one of the forces and the perpendicular distance between the lines of action of the two forces

(1cii)
Moment of couple = F x a
a = arn of couple
a = 70cm = 0.7m
moment of couple = 30N x 0.7m
= 21Nm

(1ciii)
DRAW THE DIAGRAM
Moment of force = F x d cos tan
= 20 x 15 x cos30
= 20 x 15 x square root of 3/2
= 15 square 2Nm

(2ai)
Specific heat capacity can be defined as the quantity of heat required to raise the temperature of a unit mass of 1kg through a unit rise in the temperature of 1k.

(2aii)
Specific latent heat of fusion can be defined as the quantity of heat required to change a unit mass of solid into a liquid at constant temperature measured in J1kg

(2b)
M1 = 25ᵒc M2 = 40ᵒc
Heat loss = Heat gained
M4C4 DO4 = Mw Cw DOW
Let the initial temperature be x
X – 25 = 40 – x
X + x = 40 + 25
2x/2 =65/2
X = 32.5ᵒ

(2ci)
Glass (drink ware) is made up of glass (material) with a certain amount of thickness. When you pour hot water into a glass (which is at room temperature) the inner layer of the glass will absorb heat.

(2cii)
TABULATE
|Boiling | Evaporation|
UNDER BOILING:
(i) Bubbles are formed
(ii) Source of energy needed
(iii) Boiling are fast

UNDER EVAPORATION:
(i) No bubbles are formed
(ii) Energy supplied by surrounding
(iii) Evaporation are low

(2ciii)
Power = 100w
M = 0.5kg t = ? Lv = 2.3 x 10raise power6 Jkg-1
Power = energy/time energy = p x t
Pt/p = MLV/P
T = 0.5 x 2-3 x 10raise to power6/1000
T = 1150,000/1000
T = 1150sec

(3ai)
Ultrasonic are sound waves of frequencies greater than the upper limit of the audible range for humans i.e frequency greater than 20HHz

(3aii)
(i) It can be used for imaging of internal body structures
(ii) It is also used to measure distances.
(iii) It is used to detect invisible flaws in materials
(iv) It is also used for sterilizing milk

(3bi)
An echo is sound heard after the reflection of sound waves from a plane surface

(3bii)
(i) It cause disturbance to communication

(3biii)
Velocity = 2d/t
330ms = 2d/25
2d = 330 x 2
2d/2 = 660/2
d = 330m
x = 500 – d
x = 500 – 330
x = 170m

(3ci)
DRAW THE DIAGRAM
The object should be placed between the principle focus and center of curvature of the converse lens.

(3cii)
Magnification = v (image distance)/u (object distance)
= 12cm/24cm
= 0.5

(4a)
A lighting conductor is a metallic rod mounted on a structure and intended to protect the structure from a lightning strike.

(4aii)
DRAW THE DIAGRAM

(4bi)
(i) Nature of the dielectric material
(ii) Cross sectional area of the plates
(iii) Distance between the plates

(4bii)
(i) It is used in ignition system of motor vehicles
(ii) It is used in radio circuits for tuning
(iii) It is used in the elimination of sparks when a circuit containing inductance is opened

(4ci)
V in 2uf
= 2/2+3+6 x V
2/11 x 12v = 24/11 v = 2.18v
V in 3uf = 3/11 x 12v = 36/11 v = 3.27v
V in 6uf = 6/11 x 12v = 72/11 v = 6.55v

(4cii)
Work done = qv
But v = e/d
Work done = qE/d
= 3 x 10raise to power-6 x 25/0.2 joules
= 3.75 x 10raise to power -4 joules

(5ai)
Faraday’s law states that wherever there is a change in the magnetic lines of force (e.m.f) is induced, the strength of which is proportional to the rate of change of the flex linked with the circuit.

(5aii)
TABULATE:
|D.C| A.C|
UNDER D.C:
(i) Current flows in one direction
(ii) The frequency of current is zero
(iii) Current varies with time

UNDER A.C
(i) Current flows changes direction periodically
(ii) The frequency of current is either

(5bi)
DRAW THE DIAGRAM

(5bii)
Nos of turning of primary/ Nos of turning in secondary = 6,600v/330v
= 20
(b) Efficiency = I3 E3/Ip Ep
Power = I3 x V
60w = I x 330v
I3 = 60/330 A
= 0.18A
85/100 = 0.18 x 330/Ip x 6,600
Ip = 100 x 0.18 x 330/85 x 6,600
= 0.0011A

(5c)
(a) Root mean square current is that steady current which will develop the same quantity of heat in the same time in the same resistance
(b) Resonance frequency is the frequency at which a maximum current is obtained from an a.c series circuit.
(5cii)
I = I sin wt
I = current in D.C
Therefore current in D.C =2A
(5ciii)
(i) It used in cathode ray oscilloscope
(ii) It is also used in diode value


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