## Physics Section 14

- An immersion heater of 400 watts kept on for 5 hours will consume electrical power of 2 kWh.
- Resistance of an ideal insulator is infinite.
- Reciprocal of resistivity is called conductivity.
- Circuit which gives continuously varying potential is called potential divider.
- The bulb with the thickest filament among 60W, 100W, and 200W is 200W.
- Specific resistance of a wire will depend on the type of material of the wire.
- In the given figure, the terminal potential is 12V.
- The best material for making bulb filaments is tungsten.
- If 1 ampere current flows through a 2m long conductor, the charge flow through it in 1 hour will be 7200C.
- A resistance is introduced in a circuit in series deliberately to control current.
- All electrical appliances are connected in parallel to each other between the main line and neutral wire to get the same current and potential difference.
- Resistance of a conductor depends upon nature of conductor, dimension of conductor, and physical state of the conductor.
- When a wire of uniform area of cross-section A, length L, and resistance R is cut into two parts, the resistivity of each part remains the same.
- When the same current passes for the same time through a thick and thin wire, more heat is produced in the thin wire.
- One kilowatt hour is the amount of energy delivered during one hour.
- Resistance of a superconductor is zero.
- The best material for making connecting wires is copper.
- Internal resistance is the resistance offered by the source of EMF.
- Among three bulbs rated at 40W, 60W, and 100W connected in series across 220V mains, all will burn equally brightly.
- A 40W bulb generates 144000J of heat in one hour.
- Resistance of a wire on increasing its temperature will increase with the rise in temperature.
- An electric iron marked 20 volts 500W will consume 24 kWh of units in using it for 24 hours.
- In liquids and gases, the current is due to both negative and positive charges.
- The graphical representation of Ohm’s law is a straight line.
- The resistance of a conductor at absolute zero (0K) is zero almost.
- Electrical energy is measured in kilowatt hour.
- Electrical energy is converted to heat at the rate of I^2Rt.
- A fuse is placed in series with the circuit to protect against high current.
- Among 100W, 200W, 300W, and 60W bulbs, the 60W bulb has the least resistance.
- Optical active crystals rotate the plane of vibrating light.
- In a double-slit experiment, we observe both interference and diffraction fringes.
- The property of light that does not change with the nature of the medium is frequency.
- The photoelectric effect was given by Einstein.
- Longitudinal waves do not exhibit polarization.
- A point source of light placed in a homogeneous medium gives rise to a spherical wave front.
- Nearly monochromatic light is light from a sodium lamp.
- When the crest of one wave falls over the trough of the other wave, this phenomenon is known as destructive interference.
- In Young’s double-slit experiment, if white light is used, coloured fringes will be seen.
- In an interference pattern, dark fringes are wider than bright fringes.
- The blue colour of the sky is due to scattering.
- When one mirror of a Michelson Interferometer is moved a distance of 0.5 mm, we observe 2000 fringes, and the wavelength of light used is 5000 Å.
- Wavelength of X-rays falling at a glancing angle of 30° on a crystal with atomic spacing 2 x 10^-10 for the first-order diffraction is 4 x 10^-10 m.
- In plane polarized light, vibrations take place in a direction perpendicular to the direction of propagation of light.
- X-rays cannot be polarized.
- In monochromatic red light, a blue book will probably appear to be black.
- In the double-slit experiment, if one of the two slits is covered, no interference fringes are observed.
- In the shadow of a ball, the central portion appears bright due to diffraction.
- Crystals of a material can behave as a diffraction grating.
- Sodium chlorate is not optically active.
- When light is incident normally on a thin film, the path difference depends upon both the thickness of the film and the wavelength.
- The velocity of light was determined accurately by Michelson.
- The appearance of colour in thin films is due to interference.
- A light ray traveling from a rarer to a denser medium suffers a phase change of 180°.
- Diffraction effects are more pronounced for a sharp edge.
- A diffraction grating with 500 lines per mm has a slit spacing or grating element equal to 2 x 10^-3 mm.
- Light reaches the Earth from the sun in approximately 8 minutes.
- According to Einstein, light travels in the form of photons.
- The central spot of Newton’s rings is dark.
- The locus of all points in a medium having the same phase of vibration is called a wavefront.
- Two sources of light are coherent if they emit rays of the same wavelength with a constant phase difference.
- Diffraction experiment shows that the wavelength of light is smaller than that of sound.
- When a force is parallel to the direction of motion of the body, then the work done on the body is zero.
- If a body with a mass of 2 kg is raised vertically through 2m, then the work done will be 78.4 J.
- The average power and instantaneous power become equal if work is done at a uniform rate.
- Among proton, electron, neutron, and alpha particle with the same momentum, the alpha particle has the highest kinetic energy.
- Work done by a variable force is determined by dividing force into small intervals.
- Light passing through a Polaroid becomes plane polarized.
- Diffraction fringes have a distance between them that increases as the distance from the source increases.
- A luminous object emits its own light.
- The definition of the meter in terms of the wavelength of red cadmium light was given by Michelson.
- The consumption of energy by a 60W bulb in 2 seconds is 120 J.
- The escape velocity from Earth’s surface is 11.1 km/s.
- If the moon’s radius is 1600 km and g on its surface is 1.6 m/s², the escape velocity on the moon is 2.26 km/s.
- When an arrow is released from its bow, its energy is transformed from elastic potential energy to kinetic energy.
- The work done by friction is always negative.
- The escape velocity of a body in Earth’s gravitational field is independent of its mass.
- The source of geothermal energy is the decay of radioactive elements in the Earth.
- Work done by the force of friction is always negative.
- When the speed of a moving body is doubled, its momentum increases 2 times and kinetic energy increases 4 times.
- Frictional force is not a conservative force.
- On a clear day at noon, the solar energy reaching the Earth is about 1 kW/m².
- Work done will be maximum if the angle between the force F and displacement d is 0°.
- A field in which the work done in moving a body along a closed path is zero is called a conservative field.
- Frictional force can do no work on the particle on which it acts.
- An elevator weighing 3.5 x 10^-6 N is raised to a height of 1000 m, and the work done is 3.5 J.
- The relation between horsepower and watt is 1 hp = 746 watts.
- The slope of a work-time graph is equal to power.
- The dimension of power is [ML²T⁻³].
- The dot product of force and velocity is power.
- The source of tidal energy is both the sun and the moon.
- One megawatt-hour is equal to 3.6 x 10⁶ J.
- Work has the same dimension as that of torque.
- The relation between the escape velocity V_esc and orbital speed V_o is given by V_esc = √2 V_o.
- When two protons are brought together, potential energy between them decreases.
- A man lifts vertically a weight of 40 kg through 1 m in 10 s, while a child lifts vertically a weight of 10 kg through a distance of 1 m in 1 s. The child does more work than the man.
- Work done on a body equals the change in both its kinetic energy and potential energy.
- The tides raise the water in the sea roughly twice in a day.
- The highest value of escape velocity in the solar system is for Jupiter.
- Gravitational potential energy of a body has no general formula.
- When the speed of a moving body is doubled, its kinetic energy is quadrupled.