Category Archives: Physics

How much uranium-235 would be consumed in a fission bomb with a 20-kt explosive yield?

1. How much uranium-235 would be consumed in a fission bomb with a 20-kt explosive yield?

2. A neutron collides elastically head-on with a stationary deuteron in a reactor moderated by heavy water. How much of its kinetic energy is transferred to the deuteron?

3. A buildup of fission products “poisons” a reactor, dropping the multiplication factor to 0.995. How long will it take the reactor power to decrease by half, given a generation time of 0.15 s?

Compare your answer with the 3.6×10⁶ tons of coal needed to fuel a comparable coal-burning power plant

A laser-fusion fuel pellet has mass 5.0 mg and consists of equal parts (by mass) of deuterium and tritium. (a) If half the deuterons and an equal number of tritons participate in D-T fusion, how much energy is released? (b) At what rate must pellets be fused in a power plant with 3000-MW thermal power output? (c) What mass of fuel would be needed to run the plant for 1 year? Compare your answer with the 3.6×10⁶ tons of coal needed to fuel a comparable coal-burning power plant

explore this indirect approach to particle detection by plotting the data in the table below.

1. Your roommate is writing a science-fiction novel set very far in the future, 70 Gy after the Big Bang. One of the characters is a cosmologist, and your roommate wants to know what the cosmologist will measure for the Hubble constant. What’s your answer, assuming a steady expansion rate?

2. When physicists “discover” a new particle, it isn’t by finding the particle itself in their detectors. Rather, they look for events that might indicate the particle’s decay. For a given type of event, they plot the frequency of events (number per unit energy interval) versus energy. The particle shows up as a bump or deviation from an otherwise smooth background curve. You can explore this indirect approach to particle detection by plotting the data in the table….

A rotor-resistance starter for a three-phase wound-rotor induction motor

1. A rotor-resistance starter for a three-phase wound-rotor induction motor

 

(a) adds external resistance to the wound rotor via sliprings

(b) is connected in series with the machine stator

(c) can only be used in conjunction with a double-cage rotor

(d) applies only to DC motors

2. A large synchronous motor is often started by

(a) connecting it directly to the three-phase supply

(b) pushing the rotor in the required direction before connecting the supply

(c) running it up to speed using a ‘pony’ motor before energising the rotor

(d) first switching on the rotor supply then applying the stator voltage

3.A single-phase induction motor

(a) can only be used for loads rated at less than 0.5 kW

(b) will run in whichever direction the rotor is….

Calculate the resistance of a shunt required to convert it for use as a 0–10 A ammeter.

1.The instrument of Exercise 7 is to have a multiplier connected in series with it

 

to convert it for use as a voltmeter to read up to 50 V. What will be the multiplier resistance? 2. A permanent-magnet moving-coil instrument has a resistance of 3 _, but has a 27 _ swamping resistor connected in series with it. The movement requires a current of 15 mA for full-scale deflection. Calculate the resistance of a shunt required to convert it for use as a 0–10 A ammeter. What will be the resistance of a multiplier to convert the unit for use as a 0–300 V voltmeter if the swamping resistor remains in circuit?

find the resistance of a resistor, various currents were passed through the resistor and the corresponding voltage drops across it were measured.

1.To find the resistance of a resistor, various currents were passed through the resistor and the corresponding voltage drops across it were measured. The results obtained were

 

(a) Draw to a suitable scale the graph connecting these quantities, with current values horizontal, and from the graph estimate the resistance value. (b) One serious reading error has been made; estimate what the voltage reading should be.

2.A resistor R is measured by the ammeter-and-voltmeter method, as in Figure 11.51. The ammeter and voltmeter readings are shown on the figure and the resistance of the voltmeter is 400_. Find the apparent and the true values ofR.

To what do you assign the peaks at m/z 64 and 34?

Portable mass spectrometers are now available for monitoring gaseous emissions from volcanoes.

Analyses after the eruption of the Turrialba Volcano in Costa Rica in January 2010 showed the presence of [M]+ ions (i.e. atomic ions and nonfragmented molecular ions) at m/z 64, 44, 40, 34, 32, 28 and 18. Mass spectra recorded before the eruption confirmed that the peak at m/z 64 was missing, and the peak at m/z 34 was substantially diminished.

(a) To what do you assign the peaks at m/z 64 and 34?

(b) Bearing in mind the composition of the Earth’s atmosphere, what molecular ion interferes with the detection of the volcanic emission observed at m/z 34?

(c) Volcanic gases mix with the surrounding air. Suggest what atmospheric gases give rise to the ions at m/z 40, 32 and 28.

(d) Sampling of the volcanic plume….

Describe briefly three factors which justify the need for modulation of audio frequency signals over long distances in communication.

 

 

Q. 2. (a) Describe briefly three factors which justify the

need for modulation of audio frequency signals

over long distances in communication. (b) Draw

the waveforms of (i) carrier wave, (ii) a modulating

signal and (iii) amplitude modulated wave.

 

Q. 3. (a) Give three reasons why modulation of a

message signal is necessary for long distance

transmission. (b) Show graphically an audio

signal, a carrier wave and an amplitude modulated

wave.

 

 

determine an approximate value for the average magnitude of the magnetic field in which the electron resides.

You have a new summer job with NASA and are working on astronomical observations using electromagnetic radiation that is not in the visible range. Your supervisor has explained 21­cm radiation to you and that it is used for a number of observations of interstellar hydrogen. She explains that 21-cm radiation is in the microwave region of the electromagnetic spectrum and comes from a hyperfine splitting of the electron ground state of hydrogen. It is similar to the Zeeman effect, except that it is the spin states that are split, and the magnetic field is internal to the atom: it comes from the magnetic field due to the nucleus. When the atom makes a transition from the higher state to the lower state, a 21-cm photon is emitted. Based….

What advice do you give the attorney?

You are hired as an expert witness by the attorney representing a doctor. The doctor is being sued by a patient who claimed radiation damage from the doctor’s x-ray machine. The plaintiff argues that the machine must not have been properly shielded, exposing him to dangerous radiation. Your visit to the doctor’s office shows the following results. You do indeed measure x-radiation in the doctor’s office, with a minimum wavelength of 30.0 pm. Consultation with the doctor and inspection of his x-ray machine shows that it accelerates electrons through a voltage of 35.0 kV before they strike the target, producing bremsstrahlung. What advice do you give the attorney?