Question Library

a) Differences between a d. c. generator and a moving coil galvanometer. D. C. generator moving coil galvanometer converts mechanical energy to electrical energy converts electrical energy to mechanical energy. uses split rings or commutator uses hair springs. rotation of coil is continuous rotation of coil is incomplete uses carbon brushes (as terminals) uses jeweled bearings (as terminals) (b) Eddy currents are currents induced in a conductor when subjected to varying magnetic field. Any valid additional information e.g. eddy current flows in a circular path or closed loops; eddy current generates heat; eddy current cannot flow through gaps or slots; The currents move in such a direction as to oppose the change producing them. Devices in which eddy currents are applied pointers of sensitive electric meters sensitive mass balances brakes in large electric motors speedometers in automobiles detection of cracks in railway tracks detection of metals (c) Principle on which a potentiometer is based When a steady current is allowed to pass through a uniform wire, equal lengths of the wire will have equal potential differences. OR The p.d across a length of a wire is (directly) proportional to the length provided the wire has a uniform cross section. (d) Vector diagram showing V\(_L\) with arrow V\(_C\) with arrow V\(_R\) with arrow (i) V\(^2\) = V\(_R^2\) + (V\(_L\) - V\(_C\))\(^2\) 110\(^2\) = 80\(^2\) + (40 – V\(_C\))\(^2\) (40 – V\(_C\)) = \(\sqrt{(110 + 80) (110 – 80)}\) 40 – V\(_C\) = + 75.5 V\(_C\) = 40 + 75.5 V\(_C\) = 115.5V (ii) X\(_c\) \(\frac{V_c}{I} = \frac{1}{2 \pi f c}\) C = \(\frac{1}{2 \pi fV_c}\) C \(\frac{2}{2 \times 3.14 \times 60 \times 115.5} = 45.9\muF\) (iii) \(V_L = IX_L = I \times 2 \pi fL}\) L = \(\frac{V_l}{I \times 1 \times 2 \pifVc}\) C = \(\frac{2}{2 \times 3.142 \times 60 \times 2}\) = 0.053H

(a)(i) Emission line spectra consist of distinct and separate bright lines of definite wavelengths on a dark background. Any valid additional information e.g - They are obtained when light from a luminous source undergoes dispersion and is observed directly. - When an electron moves from one energy level to another energy level, line spectra are observed - The colour of the spectra is a characteristic of the source. (ii) Line absorption spectra are obtained when light passes through a cool gas and certain wavelengths of the light are absorbed. This gives series of dark lines, each corresponding to one of the wavelengths absorbed. (b) Diagram When radiation of appropriate frequency falls on the cathode (with photosensitive surface) electrons are emitted. Because the anode is positive with respect to the cathode, the electrons are attracted to the anode. The electrons flow completes the circuit and current flows. (c)(i) Wave properties of X-rays - diffraction - interference - reflection - refraction - polarization (ii) Uses of X-rays other than in medicine to study crystal structures to detect presence of cracks in welded parts in artistic works for determining the authenticity of such works at security check points to scan X-ray spectroscopy for identifying isotopes of elements. (d) \DeltaE = E\(_i\) - E\(_f\) = - 1.6 – (- 10.4) = 8.8 e V or 1.41 x 10\(^{-18}\) J E = hf = hc/\lambda or \lambda = hc/E = 6. 6 x 10\(^{-34}\) x 3 x10\(^{8}\) 8.8 x 1.6 x 10\(^{-19}\) \lambda = 1.4 x 10\(^{-7}\) m

- Moving electrons exhibits wavelength/frequency - electrons show refraction - electrons show reflection - electrons show interference - electrons show diffraction patterns

Method of polarizing an unpolarized light; - by reflexion - by double refraction - selective absorption by crystals - polarizing by pile of plates - passing unpolarised light through a polariod

Center of gravity C = 49.5cm Mass of metre rule (MR) = 135g, d = 80cm = 0.8m h(cm) d(m) t(sec) T=\(\frac{\text{t(sec)}}{20}\) T\(^{2}\)(Sec\(^{2}\)) 40 0.8 28.0 \(\frac{28.0}{20}\)=1.40 1.9600 50 0.8 29.0 \(\frac{29.0}{20}\)=1.45 2.1025 60 0.8 31.0 \(\frac{31.0}{20}\)=1.55 2.4025 70 0.8 34.0 \(\frac{34.0}{20}\)=1.70 2.8900 80 0.8 37.0 \(\frac{37.0}{20}\)=1.85 3.4225 Slope (s) = \(\frac{\bigtriangleup {T}^{2}}{\bigtriangleup {h(cm)}}\) = \(\frac{(3.42-0.40)sec^{2}}{(80-21)cm}\) = \(\frac{3.02sec^{2}}{59cm}\) = 0.0512sec\(^{2}\)cm\(^{-1}\) K = \(\frac{S}{Q}\), Q = \(\frac{2}{25d^{2}}\) K = \(\frac {\frac{S}{2}}{25d^{2}}\) S = 0.0512sec\(^{2}\)cm\(^{-1}\), d = 50cm = 0.8cm K = \(\frac{0.0512sec^{2}cm^{-1} \times 25 \times (0.80)^{2}}{2}\) K = \(\frac{0.0512 \times 25 \times 0.6400sec^{2}cm^{-1}}{2}\) = 0.4096sec\(^{2}\)cm\(^{-1}\)m\(^{2}\) Precautions: i - ensured smooth and regular oscillations in a horizontal plane. - ensured there was no error due to parallax when reading my stopwatch. (b)i. Couple -This can be defined as two forces of the same magnitude acting in opposite directions but not on the same line. ii. Practical application of couple include: - Opening or closing taps. - Turning a spanner. - Setting a flywheel in motion about an axis through its center - Motion of a spinning spindle. - Riding/pedaling of bicycle

Table of value (observation) S/N t(min) Tc(^\circC) To(^\circC) 1 0.00 85.00 85.00 2 1.00 83.00 84.00 3 2.00 81.00 83.00 4 3.00 79.00 81.00 5 4.00 78.00 79.00 6 5.00 75.00 78.00 7 6.00 73.00 76.00 8 7.00 71.00 75.00 9 8.00 70.00 73.00 10 9.00 68.00 71.00 11 10.00 66.00 69.50 12 11.00 65.00 68.00 13 12.00 63.00 66.00 14 13.00 62.00 64.00 15 14.00 60.00 62.00 16 15.00 - 61.00 17 16.00 - 60.00 Time taken to cool from 85^\circC to 65^\circC Tin C = 11 minutes Tin D = 12.40 minutes Precautions: i - ensured there was no error due to parallax when reading my thermometer. - ensured that the liquid in the tins was gently stirred. (b)i. Silvered wall minimized radiation. Insulating cork minimized convection. (i) Factors affecting the rate of evaporation. - Temperature - Nature of liquid. - Humidity - Area of liquid surface exposed - Draught

S/N L(cm) Ii(A) L\(^{-1}\)(cm\(^{-1}\)) 1 20 1.00 0.050 2 35 0.90 0.029 3 50 0.85 0.020 4 65 0.80 0.015 5 80 0.75 0.013 When L\(^{-1}\) = 0, Ii = 0.75A \(I_o\) = 75A \(\frac{I_{o}}{I}= \frac{0.75A}{0.20A}\) = 37.5 SEE THE GRAPH ABOVE... Precautions: i - ensured there was no error due to parallax when reading my ammeter. - ensured that I removed the key after each reading. (b)i. E.m.f is the total work done in pushing one coulomb of electricity round an external resistor and the internal resistor of the source, or the total energy obtained per coulomb from a cell or battery ii. \(\frac{Ey}{Ex} = \frac{Iy}{Ix}\) Iy = 60cm Ex = 1.00v Ix = 40.cm Ey = ? \(\frac{Ey}{1.00}=\frac{60}{40}\) Ey = \(\frac{60 \times 1.00}{40}\) = 1.50.v

The silver coating on the inner bottle of a thermos flask is used to prevent heat transfer by radiation

V = wr = 2\pif r = 2 x (22)/7 x 1 x 0.6 = 3.77ms-1

The friction between the tanker and air creates charges which the chain conducts to the ground.

The force which is centripetal F = \(\frac{MV^2}{R}\) = \(\frac{5 \times 7^2}{3.5}\) = 70 Since force is 70 N when speed is 7m/s Speed = ? when force 70N is tripled → 70 * 3 = 210N 210 = \(\frac{5\timesv^2}{3.5}\) 210 \times 3.5 = 5 * v\(^2\) 735 \div 5 = v\(^2\) v\(^2\) = 147 v =12.12m/s

Smooth plane has negligible friction ∴ only the resultant of the perpendicular forces is acting on the body, which is given as F = \(\sqrt{ 6^2 + 8^2}\) = \(\sqrt{64 + 36}\) = \(\sqrt{100}\) = 10N But F = Ma ∴ a = F/M = 10/4 = 2.5 ms-1

The Kinetic Energy of a body is energy possessed by a body as a result of its motion. Hence, while in motion the kinetic energy of a body changes into potential energy as it rebounds from the floor

VR = No. of pulleys = 4 Efficiency = \(\frac{M.A}{V.R}\) cross multiply \(\frac{80}{100} * V.R\) = M.A \(\frac{80}{100} * 4\) = M.A M.A = 3.25 where M.A = \(\frac{load}{effort}\) ∴ Effort = \(\frac{1200}{3.2} * V.R\) = 375N

The condition (ii) is a condition for an equilibrium of parallel forces only while conditions (i) and (iii) are correct for both parallel and non- parallel coplanar forces. No specifications are made, so all conditions apply.