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# 2019 Neco GCE Physics| Expo Questions and Answers NECO GCE PHYSICS EXPO QUESTIONS AND ANSWERS

*Physics OBJ*
1-10: CACABDBECA
11-20: CCDBBDEECA
21-30: ECACEDACDB
51-60: CDCBCEDCCB

(1a)
Electrolysis of water uses small current for a long time while electrolysis of salt water uses a large current for a short time. Electrolysis of water in its decomposition gives hydrogen and oxygen gases due to the passage of an electric current.

2H₂O(l) + Electric energy(heat energy)  –> O₂ + H₂O

In the electrolysis of salt water like sea water, the primary aim is to produce hydrogen at the cathod.

(1b)
x/20 = 60/80
80x = 60 x 20
80x = 1200
x = 1200/80
x = 15cm
.:. The distance between the lenses = 60cm – 15cm
= 45cm

(2a)
(i) Acceleration
(ii) Velocity

(2b)
MSR = 8.5mm
VSR = 15mm
TSR = MSR + VSR
= 8.5 + 15
= 23.5mm

(5)
U1 = 4m/s
U2 = 0m/s
M2 = 60g = 0.06kg
V = 2.5m/s
M = ?
M1U1 + M2U2 = (M1+M2)V
M1(4) = (M1 + 0.06)2.5
4M1 = 2.5M1 + 1.5
4M1 – 2.5M1 = 1.5
1.5M1 = 1.5
M = 1.5/1.5
=1kg

(6a)
Draw the diagram

(6b)
(i) It is used in torches, searchlights and headlights of vehicles to get powerful parallel beams of light.
(ii) They are used as shaving mirrors to see a larger image of the face.

(10a)
Surface tension is the attractive force exerted upon the surface molecules of a liquid by the molecules beneath that tends to draw the surface molecules into the bulk of the liquid and makes the liquid assume the shape having the least surface area.

(10b)
{Pick any 2}
(i) It is in violation of the Heisenberg Uncertainty Principle. The Bohr Model considers electrons to have both a known radius and orbit, which is impossible according to Heisenberg.
(ii) The Bohr Model is very limited in terms of size. Poor spectral predictions are obtained when larger atoms are in question.
(iii) It cannot predict the relative intensities of spectral lines.
(iv) It does not explain the Zeeman Effect, when the spectral line is split into several components in the presence of a magnetic field.
(v) The Bohr Model does not account for the fact that accelerating electrons do not emit electromagnetic radiation.

(13ai)
(i) It has a small range of expansion.
(ii) It does not expand uniformly

(13aii)
When moist air near the surface if the land cools until it reaches dew point, water vapour originally present in the air begins to condense around tiny suspended dust particles in the air. They form suspended water droplets in the atmosphere. A collection of these suspended water droplets constitute a mist. Under foggy situations, motorists have to drive slowly and visibility can also be reduced that it becomes necessary to drive with the vehicle head lamps attached on even in the day.

(13b)
Such thermometer are used for measuring very high temperatures. They work on the principle of the thermocouple. When two different metals (eg copper and constantan) are joined at the ends and one end(the hot junction) is kept constant in melting ice, an electric current flows along the metals. This is the thermoelectric effect and the set up is called a thermocouple

Draw the diagram [https://i.imgur.com/H31vjkG.jpg]

The size of the current is measured by a sensitive galvanometer which is connected in series with the hot and cold junctions. This current is dependent on the difference between the temperatures of the hot and cold junctions. The galvanometer is usually calibrated to read the temperature of the hit junction directly
An instrument which uses the thermoelectric effect to measure temperature is known as a thermoelectric thermometer. Such temperatures are used in industry for measuring high temperature.

(13c)
If the temperate of a fixed mass of gas is increased at constant volume, the average kinetic energy of the molecules increases. They therefore gain more speed hence, they strike the walls of the container harder and more often in a second. This brings about an increase in the pressure of the gas. Thus, the pressure of a fixed mass of gas increases as its temperature increases at constant volume. This is a statement of pressure or Gay-lussac’s law.

(13d)
Data
T₁ = 17°c=17+273 = 290k
P₁ = 580mmHg
V₁ = 450cm³
V₂ = ?
T₂ = 5°c = 5+273 = 278k
P2 = 300mmHg
Formula
P1V1/T1 = P₂V₂/T₂
V₂  = P1V1T₂/P₂T1
V₂ = 580×450×278/300×290
V₂ = 115.035cm³

(14ai)
(i) Eclipse

(14aii)
There is a shade under a tree on a sunny day because a shadow is produced by the obstruction of light by the tree(opaque object).  The shade under a tree or a canopy, on a bright sunny day is a shadow produced by the opaque tree or canopy which obstructs light rays from the sun and prevents them from getting to the area of the shade.

(14b)
The walls and the ceiling of a shadow are covered with soft perforable boards because which can minimize the reflection of sound waves by absorbing them gently. Other methods of controlling reverberation are by changing curtains round the hall and by having more Springs in the walls.

(14ci)
It is preferred to plane mirror on the construction of periscope because it act to re-invert the image formed by the objective and present an erect image of the object to the eye piece which subsequently magnifies it.

(14cii)
It means that the angle of incidence in the denser medium is 42° when the angle of refraction is the less dense medium is 90°

(14di)
Data
M = 0.8g
L = 1.5m
F0 = 180H3
(i) F0 = 1/2L√T/M
F0² = T/4ML²
T = F0²×4ML²
T = (180)²×4×0.0008×1.5²
T = 233.28N

(14dii)
Speed = λF₀
V = L×F₀
V = 1.5×180
V = 270ms-¹

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