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(a) Application of UV radiation:
- By the human skin to synthesize or manufacture vitamin D.
- In bacteriology to kill harmful organisms.
- In the manufacture of washing powder and paints that fluoresce.
- To detect forged documents such as cheques and fake currency notes in banks.
- In burglar alarms.
- In automatic door openers.
(b)
- Photographic plates/films.
- Photocells.
- Light Dependant Resistors – LDR
Kavungya answered the question on June 3, 2019 at 06:23
- A dielectric material X is now inserted between the plates, as shown below.
State how each of the following is affected by insertion of material:
(a) the...(Solved)
A dielectric material X is now inserted between the plates, as shown below.
State how each of the following is affected by insertion of material:
(a) the potential difference (p.d) across the plates;
(b) capacitance of the set up.
Date posted: June 3, 2019. Answers (1)
- A sample of Iodine-131 contains 1000g. If the half-life of Iodine-131 is 8 days, how much of the sample will remain undecayed after 40 days?(Solved)
A sample of Iodine-131 contains 1000g. If the half-life of Iodine-131 is 8 days, how much of the sample will remain undecayed after 40 days?
Date posted: June 3, 2019. Answers (1)
- Sketch the Current-Voltage characteristic for a forward -biased diode.(Solved)
Sketch the Current-Voltage characteristic for a forward -biased diode.
Date posted: June 3, 2019. Answers (1)
- The figure below shows a thick copper conductor placed between two poles of a strong magnet. The wire is free to swing in between the...(Solved)
The figure below shows a thick copper conductor placed between two poles of a strong magnet. The wire is free to swing in between the poles.
(a) Indicate on the same diagram the direction in which the conductor swings when the switch K is closed.
(b) State one change that can be made on the set up so that the direction of swing of the conductor is reversed.
Date posted: June 3, 2019. Answers (1)
- A girl standing 120m away from a tall building claps her hands and hears an echo 0.75s later. Determine the speed of sound in air...(Solved)
A girl standing 120m away from a tall building claps her hands and hears an echo 0.75s later. Determine the speed of sound in air at this place.
Date posted: June 3, 2019. Answers (1)
- The figure below shows an incomplete circuit of an electromagnet.
Complete the circuit by drawing the windings on the two arms of the core so that...(Solved)
The figure below shows an incomplete circuit of an electromagnet.
Complete the circuit by drawing the windings on the two arms of the core so that A and B are both north poles when the switch S is closed. Indicate the direction of the current of the windings drawn.
Date posted: June 3, 2019. Answers (1)
- A current of 0.8A flows through an electric circuit. Determine the quantity of charge that passes a point in the circuit in 6 minutes.(Solved)
A current of 0.8A flows through an electric circuit. Determine the quantity of charge that passes a point in the circuit in 6 minutes.
Date posted: June 3, 2019. Answers (1)
- The figure below show two plane mirrors PQ and QR inclined at an angle of 1100.
A ray of light is incident on mirror PQ at...(Solved)
The figure below show two plane mirrors PQ and QR inclined at an angle of 1100.
A ray of light is incident on mirror PQ at an angle 560.
Complete the diagram to determine the angle of reflection of the ray in the mirror QR.
Date posted: June 3, 2019. Answers (1)
- The figure below shows an iron cylinder of length 10cm and uniform cross-section 2cm² suspended
from a spring balance with half of its length immersed in...(Solved)
The figure below shows an iron cylinder of length 10cm and uniform cross-section 2cm² suspended
from a spring balance with half of its length immersed in paraffin oil of density 0.8gcmˉ³.
(i) Show on the diagram, the forces acting on the iron cylinder.
(ii) If the density of iron is 7.5gmˉ³ determine.
(i) the weight of the iron cylinder.
(ii) the reading of the spring balance.
Date posted: June 3, 2019. Answers (1)
- Draw a clear labeled diagram of a common hydrometer which is suitable for measuring the densities of liquid varying between 1.0 and 1.2 g/cm³.(Solved)
Draw a clear labeled diagram of a common hydrometer which is suitable for measuring the densities of liquid varying between 1.0 and 1.2 g/cm³.
Date posted: June 3, 2019. Answers (1)
- A 2.0KW immersion heater is used to heat 5.0 x 10¯³m³ of water from 230C to 1000C.
Given that 30% of the heat is lost to...(Solved)
A 2.0KW immersion heater is used to heat 5.0 x 10ˉ³m³ of water from 230C to 1000C.
Given that 30% of the heat is lost to the surrounding, calculate the time needed for the heating process. Take specific heat capacity of water = 4200J/kgk, density of water = 1000kg/m³.
Date posted: June 3, 2019. Answers (1)
- A 1kg lump of solid wax is heated uniformly by a 100W heating element until after it has all melted. The graph below shows how...(Solved)
A 1kg lump of solid wax is heated uniformly by a 100W heating element until after it has all melted. The graph below shows how temperature of the wax varies with time.
Explain what is happening in the sections.
(i) WX.
XY.
Use the graph to determine
(i) the specific heat capacity of wax.
(ii) the specific latent heat of fusion of the wax.
Date posted: June 3, 2019. Answers (1)
- A trolley of height 0.2m moving on a horizontal bench of height 3.2m strikes a barrier at the edge of the bench. The object on...(Solved)
A trolley of height 0.2m moving on a horizontal bench of height 3.2m strikes a barrier at the edge of the bench. The object on top of the trolley flies off on impact and lands on the ground 2.5m from the edge of the bench as shown in the figure below.
Use this information to answer the questions that follow.
(i) Give a reason why the object on the trolley flies off on impact.
(ii) Determine the time taken by the object to reach the ground.
Date posted: June 3, 2019. Answers (1)
- The petrol air mixture in the cylinder of a car engine is ignited when the piston is in the position shown below.
Explain in terms of...(Solved)
The petrol air mixture in the cylinder of a car engine is ignited when the piston is in the position shown below.
Explain in terms of kinetic theory why the piston moves downwards.
Date posted: June 1, 2019. Answers (1)
- If the mass M of object is 500g and r is 50cm. Determine the velocity of the body if the spring balance reads 81N.(Solved)
If the mass M of object is 500g and r is 50cm. Determine the velocity of the body if the spring balance reads 81N.
Date posted: June 1, 2019. Answers (1)
- A stone is thrown vertically upwards from an edge of a platform. Eventually the stone lands without bouncing, on the ground below the platform. Taking...(Solved)
A stone is thrown vertically upwards from an edge of a platform. Eventually the stone lands without bouncing, on the ground below the platform. Taking the upward velocity to be positive, sketch the velocity-time graph of the motion of the stone.
Date posted: June 1, 2019. Answers (1)
- The mercury column in a barometer is 760mm high. Taking the density of mercury to be 13.6g/cm³, calculate the atmospheric pressure in N/m².(Solved)
The mercury column in a barometer is 760mm high. Taking the density of mercury to be 13.6g/cm³, calculate the atmospheric pressure in N/m².
Date posted: June 1, 2019. Answers (1)
- Figure below shows a non-uniform tree trunk, 9m long weighing 525N. The tree is overhanging a vertical cliff edge. A man of mass 70kg...(Solved)
Figure below shows a non-uniform tree trunk, 9m long weighing 525N. The tree is overhanging a vertical cliff edge. A man of mass 70kg is able to walk out on the tree a distance of 1.5m from the edge of the cliff before the tree begins to topple.
Calculate the distance from the cliff edge to the centre of gravity of the tree.
Date posted: June 1, 2019. Answers (1)
- An object weighs 49N on earth where acceleration due to gravity is 9.8N/kg. Find the acceleration due to gravity on another planet where the same...(Solved)
An object weighs 49N on earth where acceleration due to gravity is 9.8N/kg. Find the acceleration due to gravity on another planet where the same object weighs 40.5N.
Date posted: June 1, 2019. Answers (1)
- A string of negligible mass has a bucket tied at the end. The string is 60cm long and the buckets has a mass of 45g....(Solved)
A string of negligible mass has a bucket tied at the end. The string is 60cm long and the buckets has a mass of 45g. The bucket is swung horizontally making 6 revolutions per second. Calculate:
(i) The angular velocity.
(ii) The centripetal acceleration.
(iii) The tension on the string.
(iv) The linear velocity.
Date posted: June 1, 2019. Answers (1)