Physics Past Questions And Answers
Which of the following operations can be used to convert an alternative current dynamo into a direct current dynamo
- A. number of turns in the coil is increased
- B. strength of the field magnet is increased
- C. slip rings are replaced with split ring commutator
- D. coil is wound on a soft iron armature
(a) Define ionization potential.
(b)(i) State the three types of emission spectra.
(ii) Name one source each which produces each of the spectra stated in (b)(i).
(c) In an x-ray tube, electrons are accelerated the target by a potential difference of 80 A Calculate the:
(i) speed of the electron;
ii) threshold wavelength of the electron. [h=6.6 x 10\(^{-34}\) Js; e = 1.6 x 10\(^{-19}\) C; Me = 9.1 x 10\(^{-31}\)
d) An x-ray photon of frequency 4.5 x 10\(^{-18}\) strikes an. electron, assumed to be at rest. If t electron absorbs all the photon energy, calculate the speed acquired by the electron. [ h = 6.6 x 10\(^{-34}\) Js; Me = 9.1 x 10\(^{-31}\) kg ]
A galvanometer has a resistance of 5Ω. By using a shunt wire of resistance 0.05Ω, the galvanometer could be converted to an ammeter capable of reading 2Amp. What is the current through the galvanometer?
- A. 2mA
- B. 10mA
- C. 20mA
- D. 25mA
Temperature is the measure of the
- A. quantity of heat transferred into the molecules of an object
- B. mean kinetic energy of the molecules of the object
- C. kinetic energy of any individual molecule of the substance
- D. amount of work done by the molecules of the object
A uniform light rod is kept in horizontal equilibrium under the influence of fore forces as shown below, which of the following equations correctly represents the condition of equilibrium for the rod
- A. F1 + F2 = F3 + F4
- B. F1 + F2 - F3 + F = 0
- C. (F1 + F2)ab = (F3 + F4)cd
- D. F1a + F2b - F3c - F4d = 0
The temperature at which the water vapour present in the air is just sufficient to saturate air is
- A. Boiling point
- B. Ice point
- C. Saturation point
- D. Dew point
Which of the following factors decreases the rate of evaporation of a liquid?
- A. increase in pressure over the liquid
- B. lowering the boiling point
- C. decreasing in humidity
- D. wind
Which of the following statements about wave motion is correct?
- A. Electromagnetic waves are transverse
- B. Transverse waves do not require a medium for propagation
- C. Longitudinal waves vibrate perpendicular to the direction of travel
- D. All mechanical waves are longitudinal
The diagram below illustrates a beam of parallel rays from a distant object O, incident on one side of the total reflecting prism. Which diagram does not represent the correct path of the beam when it emerges from the prism?
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- A. W
- B. X
- C. Y
- D. Z
When an electron jumps directly from an orbit of n = 4 to n = 2,
- A. a photon is absorbed
- B. a photon is emitted
- C. two photons are emitted.
- D. two photons are absorbed