Questions about radioactivity cover fundamental concepts like defining radioactivity, the three main types of radioactive decay (alpha, beta, and gamma). They also covers the concept of half-life. They also delve into the practical aspects of radioactivity, such as measuring and detecting radiation, understanding its hazards and applications, and solving quantitative problems involving decay and remaining quantities.
Here are questions that involves introduction of radioactivity in elementary school.
2. State with a reason an essential precaution to be taken when using equipment known to emit gamma rays. (1 mk)
1. X-rays are passed through the air surrounding a charged electroscope. State what is observed. (1 mk)
2. (a) What is meant by radio – active decay? (1 mk)
(b) State a factor that leads to radio – active decay of a nucleus. (1 mk)
c) Distinguish between nuclear fission and nuclear fusion. (2 mks)
d) A radio – active source, Aluminium plate and suitable detector were arranged as below:-
(i) Before the source was introduced, the detector registered a reading of 40 counts per second. Explain this observation. (1 mk)
(ii) Name the emission from the source that was received by the detector and explain your answer.(2 mks)
(iii) Explain how the reading would be affected by removing the Aluminium. (1 mk)
( e) (i) Uranium – 235 was bombarded with a neutron and fission took place in the following manner:-
Share a lesson you wish you had learned earlier in life.
I wish i knew how to related with members of opposite sex. I would have gotten more dates and create more meaningful relationships…. Growing as an introvert, relating with other people is difficult. This is because you get bored quickly when you are with other people. So most of the time when am with people, male of female, after short while of interaction, i will find myself seeking terminating of the interacting session so that i can go back to my small world of reading.
This has costed relationships that could have changed my life…because no matter how educated you become, there are heights of success you will not attain. Education can take you places but connections with right people can take you to more places and give you fortunes.
Electric current can be generated from a variety of sources. These sources generally rely on different physical principles to create the flow of electrons.
A common source of electric currents is chemical cells and generators driven by moving water or vapor.
other sources of electricity includes:
wind driven generators
solar cells or panels
thermocouples
some crystals when under pressure(piezo electric effect)
Chemical cells, often referred to as galvanic cells or voltaic cells, are devices that convert chemical energy into electrical energy through spontaneous chemical reactions. The most common example of a chemical cell is the battery, which stores and uses electrical energy.
A chemical cell consists of two electrodes. One electrode is made of material that can undergo oxidation and is referred as the anode. The other electrode is made of material that can undergo reduction and is referred to as the cathode. These electrodes are usually placed in different solutions containing ions that can take part in the reactions.
The electrodes are immersed in an electrolyte. An electrolyte is a solution or paste that contains ions which can carry charge between the two electrodes. This electrolyte allows the movement of ions, completing the circuit and enabling the flow of electrons.
At the anode, oxidation occurs. oxidation is loss of electrons. At the cathode, reduction occurs (gain of electrons). The flow of electrons from the anode to the cathode through an external circuit is what generates electric current.
The difference in electric potential between the two electrodes creates a voltage, which is what drives the current. The voltage depends on the materials used for the electrodes and the nature of the electrolyte.
Chemical cells as source of electric current
Chemical cells that produces electromotive force as a result of chemical reactions is usually grouped into two categories. These categories are primary cells and secondary cells.
Primary cells
Primary cells are type of chemical cells that cannot be renewed once the chemicals are exhausted. This cells undergoes decays as a result of chemical reaction and once exhausted, they can only be replaced and not regenerated. Secondary cells are cells that can be renewed by recharging once chemical processes that generates current in them has been exhausted. In the next section we will be describing how various chemical cells are designed. Some of these cells includes the simple cell, the Leclanche’ cell and the dry cell.
Simple primary cells as source Electric current
The figure below shows a very simple chemical cell made of lemon, copper plate , zinc plates and conducting cables. The lemon juice acts as an electrolyte.
When the circuit is complete, the galvanometer deflects showing that current is flowing. Flowing current is a sign of existing e.m.f across the two metal plates. The galvanometer deflections drop after some time. This is because there are chemical processes in the setup that hinder further flow of current.
If similar plates were used, the galvanometer would not deflect, meaning that no current will flow. The two metals plates acting used as electrodes must have different rates of reaction when immersed in the electrolyte. Zinc is more reactive compared to copper. When these metals are immersed in an acidic medium like citric acid found in lemon, an e.m.f is set up at the other ends of the metal.
Making a simple primary cell
To make a primary simple cell, you will need the following apparatus:
Zinc plates and copper plates
A beaker containing dilute sulphuric acid
bulb
connecting wires
an ammeter with a range of 0-100 mA
procedure
Clean the metal plates using a wire brush. Then dip them into the dilute sulphuric acid as shown in the setup below.
close the switch and observe the brightness of the bulb.
Record the ammeter reading. Observe if it remains constant over a period of time. Observe formation of gas bubbles on the plates.
Add potassium dichromate to the acid and observe what happens.
Observations
Bubbles of gas form around the zinc plate when the switch is open. No bubbles form around the copper plate. This indicates that zinc is reacting with the acid faster than copper. When the switch is closed, some readings are seen on the ammeter and bulb lights dimly. Bigger bubbles of gas forms around the copper plate when the switch is closed. The gas formed is found to be hydrogen gas. Zinc metal is seen to corrode due to the acid as reaction is takes place.
The current reduces with time and soon the bulb is observed going off. Addition of potassium dichromate makes the bulb relights.
Explanations on the working of simple chemical cell
Dilute sulphuric acid exists in the form of hydrogen ions (H+) and sulphate ions (SO4 2-) as represent in the chemical formula below:
H2SO4(aq) ⇌ 2H(aq) + SO2−4
The two metal plates also known as the electrodes when dipped in the dilute sulphuric acid carries electric charges into and out of the electrolyte.
The chemical action between zinc and dilute sulphuric acid liberates electrons which flows through the connecting wire and the bulb to the copper plate. The chemical equation below shows represents the process that releases electrons:
Zn(s)⟶Zn2+(aq)+2e−
The hydrogen ions (H+) moves to the copper plate where they are neutralized by the electrons that had come from the zinc and acid reaction. This produces hydrogen gas bubbles around the copper plate.
2H+(aq)+2e−⟶H2(g)
Copper receives more electrons from the reactions of zinc and the acid. This makes the zinc plate negative and copper plate positive. Conventionally, the direction of current is from positive plate to the negative plate .
The flow of current stopped due to the defects in the cell. The two defects in this simple cell are known as polarisation and local action. polarisation and local actions are the main defects of simple cells.
polarisation
This is the accumulation of bubbles around the copper plate. This accumulation causes an insulation to the flow of current and also sets up some local cells with copper whose electron flows tends to oppose the flow of electrons from the zinc plate. The overall effect is increase in the internal resistance of the cell hence reducing the flow of current.
Addition of potassium dichromate causes some of its oxygen atoms combine with the hydrogen atoms that has formed around copper to form water. that is:
H2(g)+O2(g)⟶H20(l)
This process boosts the current flow once more but causes the electrolyte to get more diluted.
local action
Local action is a process where the zinc plate corrodes due to it’s reaction with the dilute sulphuric acid. It is promoted by the impurities in the zinc plate. Local action can be minimized by use of pure zinc or coating the zinc metal with mercury in a process known as amalgamation.
The Leclanche’ cell as source of Electric current
Leclance’ cell is an improvement from the simple cell. It is a cell where defects in simple cells have been minimized. The basic structure of the leclanche cell is as shown below.
the structure of a Leclance’ cell
From the diagram, the carbon rod (positive terminal) is covered with mixture of manganese (IV) oxide and carbon powder. The manganese (IV) oxide acts as a depolariser. It reacts with the hydrogen gas formed on the carbon rod to produce water hence slowing down defect of polarisation. This process is however slow hence large currents cannot be drawn out of this cell steadily for a long time. The carbon powder increases the effective area of the plate which reduces the opposition to the flow of current. remember that, the larger the area of conductor, the less the electrical resistance in a conductor.
The zinc plate is dipped in ammonium chloride solution, which converts zinc to zinc chloride when the cell is in operation. Local action defects has not been removed from this cell.
Leclanche cell is most suitable for devices that don’t need current to be drawn from the cell for a long time. For example operating electrical bells and telephone boxes. Leclanche cell has longer life compared to the simple cell.
The Dry Cell
Dry cell is a primary chemical cell without a liquid as an electrolyte. Instead of ammonium chloride solution used in the leclanche’ cell, ammonium chloride jelly is used.
The figure below shows the structure of a dry cell.
The dry cell
Manganese (IV) oxide and carbon powder are used as depolariser in the cell. The hydrogen gas produced at the positive terminal meets with oxygen atoms in the depolariser to form water. This makes the cell become wet after use.
The zinc case acting as the negative electrode corrodes due to it’s reaction with ammonium chloride forming zinc chloride. This makes local action remains a defect in a dry cell.
A dry cell, like other primary cells, cannot be renewed when chemical actions that produces current are complete. A new dry cell has an e.m.f. of about 1.5 V.
commercial dry cell
Large currents should not be drawn from the dry cell within a short time. Short circuiting the dry cell can also ruin it. A dry cell must be stored in dry places since it can be damaged by moisture through chemical process.
Dry cells are commonly used in torches, calculators and radio receivers as their source of electric current.
Reflection of straight and circular waves occurs when waves meet circular or straight reflectors.
When plane waves hit a surface at an oblique angle, they are reflected. This reflection follows the laws of reflection. All waves can be reflected.
Water waves are reflected from obstacles in their paths the same way as light and sound waves. All reflections obeys the laws of reflection.
See the figure below.
The laws of reflection states that:
The angle of incidence i equals the angle of reflection r.
The incident ray, reflected ray, and normal at the point of incidence all lie on the same plane.
Reflection of waves obeys the laws of reflection.
Plane waves normal to the reflecting surface
Plane waves incident onto a straight reflector at 90o .to the surface will be reflected such that they are perpendicular to the reflecting surface. see the figure below:
straight and circular waves: reflection of plane waves by curved reflectors
When plane waves falls onto a concave reflector, they converge to a point in front of the reflecting surface. This is the same way all rays of light parallel and close to the principal axis converge after reflection. The plane waves will be reflected as circular waves that seems to change direction after the converging point. see the figure below:
straight and circular waves: plane waves incident to convex(diverging) reflector
When plane waves meets a convex reflector. they are reflected such that they appear to diverge diverge. from a point behind the convex surface. The waves reflected from convex reflector has virtual principal focus.
circular waves against a straight reflector.
Circular waves incident to a straight reflector will be reflected as circular waves. These waves seem to have a converging point behind the plane reflector. see the figure below:
circular waves incident to the concave reflector straight up and moves as plane waves after reflection. See the figure below.
Electrostatics is a branch of physics that deals with behavior and properties of charges that are not flowing. When we subject materials to mechanical friction force against other materials, the electrons near the surface jump out from one material and become lodged to the other material. In other word, when materials rub each other, electrons are transferred. The transfer of electrons is what is referred as charging of the material.
Materials are made from matter and matter is made of atoms. Atoms are considered to be very tiny particles whose size is in the order of 0.1 nanometers and that cannot be divided further. Atom is considered as the blue print of every matter whether it is a gas, liquid or solid. They are the basic structures that are joined together to make molecules that composes matter.
Electrostatics: Structure of an atom
Atom is made up of two parts, a central core called nucleus and outer orbits where electrons goes around the nucleus. The nucleus contains particles called protons and neutrons closely and tightly packed inside.
Protons carries a positive charge whereas electrons carries negative charges. Neutrons carries no charge.
The number of protons and electrons in an atom are equal in number such that the resultant charge is zero. This is because there are equal number of positive charge as there are negative charge so that they cancel out each other making the overall charge in an atom to be zero.
Causes of electrostatics charging
In some materials , electrons are not tightly bund to the nucleus and so when given some little energy, they tend to jump out of the atom. When two materials are rubbed against each other, the heat energy developed due to friction may cause some loosely held electrons from one material to move and be transferred to the other material. Some materials easily losses elecrons whereas others readily accepts electrons during friction.
Materials that losses electrons are said to be positively charged because they have overall more positively charged protons compared to electrons.
Materials that gains electrons are said to be negatively charged because they have overall more negatively charged electrons as compared to the protons. As an example, when polythene is rubbed against flannel clothe, it gains electrons and becomes negatively charged . Consequently, flannel clothe becomes positively charged because it looses some of its negatively charged electrons to polythene.
Glass will loose electrons to silk when they are rubbed together making the glass to gain positive charge and silk to be negatively charged.
The following has been observed when materials have been charged by friction.
Excess negative charge on one body is equal to excess of positive charge on the other body and so no new charges is ever created. In electrostatics charges are never created, they are only transferred.
Some materials will always acquire they same type of charge during charging and so it may be possible to predict the charges on materials after you rub them together.
The quantity of charge in some cases maybe small and in some cases charges may escape before they are detected. When charging by friction, the idea environment is a dry atmosphere and clean charging bodies to avoid discharge.
Some Experiments to explain electrostatic charges
Take a polythene strip and rub it against silk and then take the strip near a thin stream of flowing tap water as shown:
When a charged strip is brought near a thin stream of water, the of water is strongly attracted to the polythene as shown.
when a plastic comb, pen or plastic ruler is rubbed against your clothe or hair, it is observed to attract small pieces of paper as shown.
A household mirrors and windows attract dust and other particles when wiped with a dry clothe because of electrostatic charges.
All the above observations are as a result of electrostatic charges.
There are two types of charges namely negative and positive charges. The SI unit of charge is the coulomb(c).
1 Coulomb = 1000 millicoulombs
millicoulomb = 1000 microcoulombs
1 coulomb = 1000 000 microcoulombs
The basic law of charges
The basic law of charges states that like charges repel, unlike charges attract. In this lesson, we will discuss physics experiments that can verify this basic law.
Experiments to verify the law of charges
To investigate what happens when two charges bodies are brought together, you may need the following apparatus:
glass rods
silk cloth
Silk Thread
Stand
Bunsen burner
polythene rod
duster
To investigate the law of charges in electrostatics, use the following procedure:
Dry glass rod by running it over a Bunsen flame a few times.
rub the dry rod with a silk and then suspend it by a thread on a stand
Dry a second glass rod over bunsen burner and rub it with silk cloth.
Hold the second glass rod close to the first suspended glass rod as shown.
With the glass rod still suspended, bring a polythene rod rubbed with fur close to it as shown.
Observations from experiments on law of charges
when a charged glass rod is moved close to a suspended charged glass rod, they were observed to repel each other.
When a charged polythene rod is moved close to a suspended charged glass rod, they were observed to repel each other.
Explanation
The glass rods were rubbed with the same material and so they acquired same positive charge . The repulsion between them implies that like charges repel each other.
When polythene rod was rubbed with fur, it acquired negative charge. When the charged polythene rod attracts the positively charged glass rod, it shows that opposite charges attracts each other. The above experiment and observations brings us to conclusions on charges with the basic law of charges that states that like charges repel while unlike charges attract.
The basic law of charges states that like charges repel, unlike charges attract. In this lesson, we will discuss physics experiments that can verify this basic law.
Experiments to verify the law of charges
To investigate what happens when two charges bodies are brought together, we need the following apparatus:
glass rods
silk cloth
Silk Thread
Stand
bunsen burner
polythene rod
duster
To investigate the law of charges, use the following procedure:
Dry glass rod by running it over a Bunsen flame a few times.
rub the dry rod with a silk and then suspend it by a thread on a stand
Dry a second glass rod over bunsen burner and rub it with silk cloth.
Hold the second glass rod close to the first suspended glass rod as shown.
With the glass rod still suspended, bring a polythene rod rubbed with fur close to it as shown.
Observations from experiments on law of charges
when we moved a charged glass rod close to a suspended charged glass rod, we observe them to be to repelling each other.
When a charged polythene rod is moved close to a suspended charged glass rod, they were observed to repel each other.
Explanation
The glass rods were rubbed with the same material and so they acquired same positive charge . The repulsion between them implies that like charges repel each other.
When polythene rod was rubbed with fur, it acquired negative charge. When the charged polythene rod attracts the positively charged glass rod, it shows that opposite charges attracts each other. The above experiment and observations brings us to conclusions on charges with the basic law of charges that states that like charges repel while unlike charges attract.
Atomic structure describes how an atom is built from protons, neutrons, and electrons. At the center of the atom is the nucleus, containing positively charged protons and neutral neutrons. Negatively charged electrons orbit the nucleus in shells, with their negative charge attracting the positive protons to hold the atom together. Atoms are electrically neutral because they have an equal number of protons and electrons.
The nucleus of an atom has a specific number of protons and neutrons. The number of protons in the nucleus is called the atomic or proton number. When the number of protons and the number of neutrons in the nucleus are summed up, the resultant number is known as the mass number. Mass number is also known as the nucleon number.
Different atoms has different mass number. For example, hydrogen atom has mass number of 2, meaning it has 1 neutron and 1 proton in it’s nucleus. A neon atom has mass number as 20 having 10 protons, 10 neutrons and 10 electrons. similarly, helium atom has mass number 4 with 2 protons, 2 neutrons and 2 electrons.
describing the mass number in atomic structure
If a certain atom X has atomic number Z with N neutrons and mass number A, then we can express it as:
$$^{A}_{Z}X \ \ \ where A = Z + N$$
Thus neon, helium and hydrogen atom will be represents as:
where Ne is neon atom, He is the helium atom and H the hydrogen atom.
There exists atoms that have the same atomic number but with different mass numbers. Such atoms are said to be isotopes. For example carbon-14 and carbon-12 has mass number 14 and 12 respectively but both has atomic mass 6.
The two will be represented as shown:
$$^{12}_{6}C \ \ and \ \ ^{12}_{6}C $$
Stability of the nuclear in atomic structure
A nuclear is said to be stable when a ratio of it’s proton to neutron number is 1 or close to 1. that is
$$\frac{\text{mass of proton}}{\text{mass of neutron}}=1$$
As atoms gets heavier, there is a marked deviation from this ratio, with the neutron number exceeding that of protons. This causes the nucleus to be unstable and hence increases chances of the nuclear disintegrating to gain stability. A graph of number neutrons N against number of protons Z for different nucleus is illustrated below.
From the graph, it is observed that the stable nuclides are outside the stability line.
Nuclides above the stability lines have too many neutrons. Such nuclides decays in such a way that the number protons increases.
Nuclides below the stability line have too many protons . Therefore, they decay to decrease the number of protons.
Some applications of C.R.O includes measuring of electrical potential as a voltmeter, television displays and in measuring frequency of signals.
applications of C.R.O as a voltmeter
C.R.O can be used as a voltmeter when it time base circuit is switched off and the voltage to be measured is connected across the Y-plates while the X-plates are earthed.
The vertical displacement of the bright spot on the screen is measured and the sensitivity of the C.R.O is adjusted to determine number of volts per units of displacement along the vertical scale.
The number of volts per unit of division is the sensitivity. The voltage can the be determined as:
Voltage = displacement x sensitivity
Sensitivity is adjusted using the Y-gain knob which automatically connects the input signal through an application system.
Amplification system ensures that even very signals are raised to the levels where they cause measurable deflection of the beam.
application of C.R.O as a voltmeter is considered a superior voltmeter compared to convectional ones because of the following reasons:
can measure large voltages without being damaged
can measure both direct and alternating voltages
Has infinite resistance hence takes no current meaning that it rarely interferes with the circuit into which it is being connected.
It responds instantaneously unlike ordinary meters whose meters swings momentarily about the correct reading due to inertial.
Example Problem on usage of C.R.O as a voltmeter
A D.C voltage of 80V when applied to the Y-plates of a C.R.O causes a deflection of the spot as shown in figure below:
(i) Determine sensitivity of the y-gain
(ii) show what will be formed on the screen if an a.c of peak voltage 64V
is fed onto the Plates.
solutions
(i)
spot deflection on the screen from the center of the screen = 5 divisions
Voltage in a.c with be a straight line 4 divisions above the central line and 4 divisions below it as shown below
Example applications of C.R.O
The Y-gain of a CRO has a sensitivity of 500V/div. An a.c voltage of 2500V is connected across the Y-plates. show what is observed on the screen.
solution
Voltage = sensitivity x number of divisions
We need to determine the number of divisions that a signal will be displaced vertically.
$$\text{Number of divisions} = \frac{voltage}{sensitivity} = \frac{2500 V}{500 V / div} = 5 divisions $$
Numberofdivisions=Voltagesensitivity
=2500V500v/div=5divisions
Hence a straight vertical line will be formed on the screen covering 5 divisions above the x-axis and 5 divisions below it as shown
applications of C.R.O to measure frequency of an a.c signal
The signal is fed into the Y_plates of a C.R.O with the time base on. The time base control is then adjusted to give one or more cycles of the input signal on the screen. By adjusting the time base control, we can determine the number of cycles made on the screen from the periodic time T. Frequency can then be calculated from f=1/T.
Example question on applications of C. R.O
Figure below shows a trace on the screen for an signal connected to the Y_plates of a CRO with time base on.
Given that the time base control is 20ms/div and the Y-gain is at 80V/div, determine:
(i) frequency of the a.c signal
(ii) The peak voltage of the input signal
solution (i)
Time base settings is 20ms/div
Number of waves shown on the screen =3.25
7 div is covered by 2.5 waves.
1 wave = 7.0/2.5 = 2.8 divisions
Time taken to complete 1 wave (periodic time) = 2.8 div x 20ms/div = 56ms = 56 x 10-3s
Frequency=1T
And so the frequency will be given by:
Frequency=156∗10−3s
0.01786 x 103 Hz =17.86 Hz
solution (ii)
Y-gain =80div
Approximate deflection as about 2.2 divisions as per the graph
The term “properties of cathode rays” refers to the various physical characteristics and behaviors observed when cathode rays are studied under different conditions.
properties of cathode rays includes:
They travel in a straight line
causes fluoresce or glow to certain materials
they are charged
possesses kinetic energy
pass through thin materials demonstrating their ability to penetrate objects to varying degrees. This depends on the material’s density and the energy of the rays.
ionize gases
The charge-to-mass ratio of cathode rays (electrons) is relatively high. A property used to identify the electron and distinguish it from other particles.
Deflection by Magnetic Fields
Showing that cathode rays travels in a straight line
When an opaque object is placed between the screen and the cathode in the path of the cathode rays, a sharp shadow is cast on the screen.
Cathode rays causes certain substances to glow or fluoresce
Fluoresce materials are materials that glows when electromagnetic energies falls on them. such materials includes zinc sulphide, Fluorescein, Rhodamine, Coumarin, Acridine Orange and Quantum Dots.
when cathode rays falls on screen coated with the fluoresce materials, the fluoresce material glows.
showing that cathode rays are charged
Cathode rays are deflected by both magnetic and electric fields.
Inside the magnetic field, the cathode rays are deflected towards the positive plate showing that they are negatively charged. Remember that opposite charges attract while while same charges repel from the basic law of charges. see the figure below:
When cathode rays passes through magnetic field, they are deflected in the direction determined by Fleming’s left-hand rule. The deflection in magnetic field shows that they are negatively charged as shown in figure below.
Cathode rays have kinetic energy
The deflection of cathode rays in a magnetic field shows they are moving, and therefore possess kinetic energy. By measuring how much the cathode rays bend in the magnetic field, you can calculate their velocity. Using the velocity, you can compute the kinetic energy of the cathode rays.
When cathode rays are suddenly stopped by a metal target, they can produce x-rays. This confirms that they are actually a stream of fast moving electrons.
Exam Questions on properties of cathode rays
Figure 14 shows a cathode ray tube. A metal plate is placed between the anode and the screen.
(I) State with reason what would be observed on the screen when the cathode rays are produced. (2 marks)
(ii) State the effects on the cathode rays produced when the anode is increased. ( 2 marks)
Exam questions on Cathode rays are an important topic in physics and chemistry. They test knowledge on key curriculum areas that includes:
Atomic Structure
Electricity and Magnetism
Properties of Matter
Electron beams
Charge-to-mass ratio (e/m)
Millikan’s oil drop experiment
etc.
below are questions commonly tested in physics examinations on this topic;
1. The figure 1 below represents a cathode ray oscilloscope (C.R.O) (i) Name the parts labeled A and B (2 marks)
Figure 1
A.…….………………………………………………………………………………………… B.…….…………………………………………………………………………………………. ii) What are the functions of parts labeled C and D (2 marks) C ………………………………………………………………………………………………… D …………………………………………………………………………………………………. iii) Explain how electrons are produced. (1 mark) …………………………………………………………………………………………………… ……………………………………………………………………………………………………. iv) Give a reason why the tube is evacuated. (1 mark)
2. State the function of the grid in a cathode ray tube (CRT) (1 mark)
3. State two reasons why the CRO is a more accurate voltmeter than a moving coil voltmeter. (1 mark)
4. Figure 2 shows a cathode ray entering into a region between two charged plates.
Complete the diagram to show the path of the ray in the electric field. (1 Mark)
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