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Modern Physics

The Electron:

Section 1.

Q1. Name 3 properties of the electron.

Q2. What is the function of the deflecting plates in a Cathode ray tube?

Q3. What is the makeup of the screen in the CRT?

Q4. What is thermionic emission?

Q5. What happens to the kinetic energy of an electron as it hits the screen on a CRT?

Section 2.

Q1. What happens to a charge when it enters a high voltage?

Q2. If an electron enters a high voltage of 10KV find the energy it acquires.

Q3. If an electron is in a voltage of 9.5kv find the speed at which it hits the screen of a CRT.

Q4. What are cathode rays?

Q5. Give some properties of cathode rays.

Section 3.

Q1. Explain what is meant by the photoelectric effect.

Q2. Describe an experiment in which you could demonstrate the photoelectric effect.

Q3. What component of light is the most important in the photoelectric effect?

Q4. Write down an expression that describes Einstein’s photoelectric law.

Q5. Describe Einstein’s photoelectric law in words.

Section 4

Q1. Define the work function and the threshold frequency of a metal. Write down equations that would help you find them.

Q2. What effect does increasing the frequency of light have on the photoelectric effect?

Q3. What would the effect be of increasing the light intensity during the photoelectric effect?

Q4. If light has a frequency of 12X10¹⁴ Hz find the energy of the light.

Q5. If light has a wavelength of 869nm find the energy of the light.

Section 5.

Q1. Give some uses of Cathode ray tubes.

Q2. What are X-rays?

Q3. Draw a labelled diagram of an X-ray tube.

Q4. Explain why a target with a high melting point is used in the X-ray tube.

Q5. Give some applications of the photoelectric effect.

Section 6.

Q1. If light with frequency 10X10¹⁴Hz hits a metal with threshold frequency of 9X10¹⁴Hz calculate the velocity of the emitted electrons.

Q2. Who named the electron & who discovered the size of the charge on it?

Q3. What is a photocell?

Q4. If an electron moves in a circle of radius 3X10^-6m and has a speed of 5x105ms^-1 find the force on the electron.

Q5. Define the electron volt.

Section 7.

Q1. Find the force on an electron which is in a magnetic field of magnetic flux density 5 Tesla, when it has a speed of 5X10⁷ms^-1.

Q2. Find the force on an electron in a magnetic field of magnetic flux Density 7T and a velocity of 20m/s.

Q3. If a photon of light has energy of 2x10^-18j find the frequency and the wavelength of the light.

Q4. If a photon of light has energy 6eV find the frequency and wavelength of the light in question.

Q5. Light passes through a diffraction grating of 600 lines per mm. The angle between the first order image on the right and the first order image on the left is 22 degrees. Find the energy of the light.

Q6. Convert the following electron volt values into Joules.

(1) 25 eV (2) 10 eV (3) 1 eV

Q7. Convert the following joule values into Electron volts.

(1) 2j (2) 1X10^-19j

Section 8.

Q1. An electron has energy of 300X10^-18j of energy. Express this energy value in KeV.

Q2. Explain Einstein’s Photoelectric law in words but also give an expression that describes it.

Q3. If and electron enters a voltage of 10KV find the frequency of the X-ray that will be produced when it hits a metal target.

Q4. Find the wavelength of light that has energy of 1x10^-20j.

Q5. An electron enters a magnetic field of flux density 4.2T at a velocity of 1x10⁴m/s find the force acting on the electron. How does the electron move? Find the radius of the pattern it carves out.

Atoms & radioactivity

Section 1.

Q1. What are Alpha particles?

Q2. Explain the Rutherford experiment which investigates the structure of the atom with regard to the process he undertook the results he observed and the conclusions he drew.

Q3. Explain the significance of the atomic number and the mass number for elements on the periodic table.

Q4. The AMU is used to describe the mass of atoms. What does AMU stand for and what is 1 AMU in kg?

Q5. Using the maths tables find the mass in kg of a ¹H₁ , ²H₁, ³H₁ atoms. All of these atoms are are Hydrogen in one from or another. What are these kind of variations on the same atoms known as? These three in particular have individual names, write down the names of these elements.

Section 2.

Q1. Explain the following two terms. Continuous Spectra...Line Spectra.

Q2. What is the study of these two types of phenomenon known as?

Q3. If an electron jumps from energy level E1 to energy level E2 and then falls back to E1 with a level energy difference of 1X10^-20j. Find the frequency of the photon produced.

Q4. How could the electron in Q3 been given this extra energy?

Q5. Why are line spectra considered to be so valuable to Physicists.

Section 3.

Q1.What is radiation?

Q2. Name the three forms of radiation.

Q3. Explain how the three types of radiation you mentioned in Q2 come about.

Q4. Describe an experiment to show the penetrating power of the three types of radiation.

Q5. Describe an experiment to show that there are infact three different types of radiation.

Section 4.

Q1. Name two devices that can be used to detect radiation.

Q2. Of the two devices you named in Q1. Describe the principal of operation of one of them.

Q3. Write an expression that describes beta radiation.

Q4. If a radioactive isotope ²³⁸U₉₂ decays to ²³⁰Th₉₀ How many alpha and Beta particles has it lost?

Q5. Show ²³⁰Th₉₀ decaying by 2 alpha particles and a Beta particle.

Section 5.

Q1. Write an expression that shows ²³⁸U₉₂ losing an Alpha particle.

Q2. If a radioactive element loses a beta particle in which direction will it go on the periodic table. Explain your thinking.

Q3. If a radioactive atom undergoes alpha emission in which direction will the resulting atom go on the periodic table. Explain your thinking.

Q4. If a gamma radiation photon is emitted from the nucleus of a radioactive atom with a frequency of 2X10²⁰Hz what is the wavelength and the energy of the emitted photon?

Q5.

Section 6.

Q1. Explain the Rutherford experiment.

Q2. Name the three types of radiation and say what they are made up of.

Q3. Show experimentally that there are three. Show penetrating power.

Q4. Show ²³⁸U₉₂ disintegrating by losing an alpha and beta particle.

Q5. A radioactive isotope has a half life of 10 years how much is left after 30 years? An alpha emitter has a half life of 8X10⁸years find the number of particles being emitted from a sample containing 2.5X10²⁵atoms.

Q6. Name two instruments used to detect radiation. Explain one.

Q7. Give some properties of the electron.

Q8. Explain the term thermionic emission.

Q9. After thermionic emission an electron enters a potential difference of 8kv. What energy does the electron gain? What speed is it travelling leaving the high voltage? If the electron then enters a magnetic field at right angles to the field and starts to move in a circle of radius 1x10^-8m what is the strength of the magnetic field?

Q10. Explain the photoelectric effect. If this occurs to a metal with a work function of 2ev as a result of light with wavelength 600nm falling on it, give the kinetic energy of the emitted electron.

Q11. What is Einstein's photoelectric law?

Fission Fusion and Nuclear energy

Section 1.

Energy is released in a fission reactor when a chain reaction occurs in the fuel rods.

What is meant by fission? Name a material in which fission occurs.
Describe how a chain reaction occurs in the fuel rods.
Explain how the chain reaction is controlled.
What is the purpose of the shielding?
Name a material that is used as shielding.
Describe what happens to the coolant when the reactor is working.
Give one effect of a nuclear fission reactor on the environment.
Give one precaution that should be taken when storing radioactive material.

Section 2

What is radioactivity?
The diagram shows the basic structure of a nuclear reactor.
A nuclear reactor contains (i) fuel rods, (ii) control rods, (iii) moderator, (iv) heat exchanger.
Give the function of any two of these.
In a nuclear reactor, energy is released by nuclear fission when a chain reaction occurs.
What is nuclear fission?
What is a chain reaction?
Thick shielding is placed around a nuclear reactor because of the penetrating power of the radiation emitted.
Name three types of radiation that are present in a nuclear reactor.
Name an instrument used to detect radiation.
Plutonium is produced in a nuclear reactor. It is a highly radioactive substance with a very long half-life. When the fuel in a nuclear reactor is used up, the fuel rods are reprocessed to remove the plutonium.Give two precautions that are taken when storing the plutonium.

Section 3.

A nuclear reactor is a device in which a sustained chain reaction takes place.

From each nuclear fission, only one (on average) of the emitted neutrons hits another nucleus to cause another fission. The power output from a sustained nuclear reaction doesn’t grow, but is constant.

Explain the underlined terms.
A substance called a moderator is mixed with the fuel in a nuclear reactor. Control rods are used to control the rate of the reaction.

Give an example of a moderator.

Explain why a moderator is needed in a nuclear reactor
Explain how the control rods affect the rate of the reaction.
A heat exchanger is used in a nuclear reactor.

Explain how the heat exchanger operates.

Why is it necessary to use a heat exchanger?
Plutonium is produced in a fission reactor when one of the neutrons released in the fission reaction converts uranium–238 into plutonium–239 with the emission of two beta-particles.

Write an equation for this nuclear reaction.

Each fission of a uranium–235 nucleus produces 202 MeV of energy.

Only 35% of this energy is used to generate electricity.

How many uranium–235 nuclei are required to undergo fission to generate a constant electric power of 1 GW for a day?

The following is the nuclear equation of a fission reaction explained by Meitner.

²³⁸U₉₂ + ¹n₀ >>>>> ¹³⁹Ba₅₆ + ⁹⁷Kr₃₆ + 3(¹n₀)

(Nuclear masses: U–238 = 3.9529 ×10–25 kg; Ba–139 = 2.3066 ×10–25 kg; Kr–97 = 1.6099 ×10–25 kg)

Calculate the energy released during this reaction.

Q3. Give some properties of the electron. Explain the term thermionic emission.

After thermionic emission an electron enters a potential difference of 8kv. What energy does the electron gain? What speed is it travelling leaving the high voltage? If the electron then enters a magnetic field at right angles to the field and starts to move in a circle of radius 1x10-8m what is the strength of the magnetic field?

Explain the photoelectric effect. If this occurs to a metal with a work function of 2ev as a result of light with wavelength 600nm falling on it, give the kinetic energy of the emitted electron.