## Physics Section 8

- Electromagnetic waves transport energy.
- Electromagnetic waves emitted from an antenna are transverse.
- Time taken for the potential difference across the capacitor to reach 300V is 0.9 seconds.
- The r.m.s value of an alternating current is represented by the square root of the mean value of I^2.
- An alternating current of frequency and amplitude twice that of the given current is represented by I = 2Iâˆ«Sin(2Ï€t).
- In a pure resistor circuit, the voltage and current have zero phase difference.
- When A.C current passes through a capacitor, the current leads voltage by a phase angle of 90 degrees.
- In a capacitive circuit, the current leads voltage by Ï€/2.
- A 100Î¼F capacitor with a 12V source in series at a frequency of 50Hz offers a capacitive reactance of 32Î©.
- Inserting a glass plate between capacitor plates and a lighted bulb increases the bulb’s brightness.
- Impedance of an inductive coil at frequency f is (R^2 + 4Ï€^2f^2L^2).
- An ammeter in an AC circuit measures the RMS value of the current.
- When a pure inductor and capacitor are connected in parallel, the potential difference across both is the same.
- Self-inductance of a coil with an induced emf of 2V at a rate of 4 As^-1 is 0.5H.
- The frequency of a circuit with capacitance C and resistor R is 1/RC.
- The peak value of the potential difference across a 10Î© electric heater connected to 220V 50Hz mains supply is 220âˆš2V.
- A choke is used as resistance in AC circuits.
- At resonance, the power factor in an L-C-R series circuit is 1.
- An A.C series circuit with 4Î© resistance and 3Î© inductive reactance has an impedance of 5Î©.
- An inductive coil with resistance of 100Î© and a phase angle of 45Â° has an inductance of 16mH.
- Ohm’s law holds for peak, effective, and instantaneous values of voltage and current in AC circuits.
- The phase angle between voltage and current in an AC circuit with only resistance is zero.
- V^2 = VR^2 + (VL – VC)^2 in an LCR series circuit.
- The average power dissipated per cycle in a resistor with a voltage V = V0cosÏ‰t is V0^2/âˆš2R.
- When two identical coaxial circular loops carry equal currents in the same direction, the current in each decreases.
- An inductor may store energy in its magnetic field.
- Vector addition obeys commutative, distributive, and associative laws.
- The direction of a vector in space is specified by three angles.
- A vector can be multiplied by a number, which may be dimensionless, dimensional scalar, or negative.
- The unit vector n^ is along a normal on a surface.
- The rectangular coordinate system is also called the Cartesian coordinate system.
- The maximum number of rectangular components a vector can have is 3.
- CosÎ¸i^ + SinÎ¸j^ is a unit vector in the direction at angle Î¸ with the x-axis.
- A vector A = 2i^ + 2j^ + 3k^ has direction at 45Â° with the x-axis and magnitude 2.
- An angle between two vectors A and B can be determined by their dot product.
- Two forces of equal magnitudes in opposite directions and making an angle of 120Â° with each other are in equilibrium.
- Three coplanar forces keeping a body in equilibrium are concurrent.
- Torque is the turning effect of force.
- It is easier to turn a steering wheel with both hands because the couple acts on the wheel.
- The cross product of i^ x j^ is equal to 1.
- The unit vector in the direction of vector A = 2i^ – 2j^ + k^ is (2i^ – 2j^ + k^)/3.
- The cross product of two vectors is a negative vector when they are rotated through 270Â°.
- Both tanÎ¸ and tan(180Â° + Î¸) have positive values in the first and third quadrants.
- The magnitude of i^. (j^ x k^) is 1.
- A = Ax i^ + Ay j^ + Az k^, B = Bx i^ + By j^ + Bz k^, then A. B = Ax Bx + Ay By + Az Bz.
- A body in equilibrium may be at rest or in uniform motion.
- The maximum value of the static frictional force is Î¼sN.
- Friction opposes the relative motion between any two objects.
- The weight of a body acts through its center of gravity.
- The acceleration due to gravity decreases with increasing altitude above the Earth’s surface.
- An object in motion has a tendency to remain in motion at the same speed in the absence of an external force.
- The mass of an object remains constant regardless of its location.
- The force of gravity between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance.
- The acceleration due to gravity is the same at all points on the Earth’s surface.
- Inertia is the property of an object to resist changes in its state of motion.
- The momentum of an isolated system is conserved.
- The SI unit of momentum is kg.m/s.
- Work done by a force is scalar and has no direction.
- The unit of energy and work is joule.
- Energy can be transformed from one form to another, but it cannot be created or destroyed.
- Power is the rate of doing work or transferring energy.
- The momentum of an object is the product of its mass and velocity.
- The weight of an object is the force with which it is attracted towards the Earth.
- A change in momentum produces a force on an object.
- A body at rest will remain at rest unless acted upon by an external force.
- The acceleration of an object is directly proportional to the net force applied to it and inversely proportional to its mass.
- The quantity 1 kg m/s^2 is equivalent to 1 newton.
- An object will float in a liquid if its average density is less than the density of the liquid.
- The temperature remains constant during a change of state of matter.
- The average kinetic energy of molecules increases with an increase in temperature.
- The absolute temperature scale is the Kelvin scale.
- Heat energy is transferred from a region of higher temperature to a region of lower temperature.
- The heat required to raise the temperature of 1 gram of water by 1 degree Celsius is called a calorie.
- The process of a gas changing directly from a solid to a gas is called sublimation.
- The specific heat capacity of a substance is the amount of heat required to raise the temperature of 1 gram of the substance by 1 degree Celsius.
- The Kelvin scale of temperature is based on the Celsius scale.
- The SI unit of heat is the joule.
- The pressure of a gas is inversely proportional to its volume if the temperature and quantity of gas are held constant.
- Boyle’s law relates the pressure and volume of a gas at constant temperature.
- The velocity of gas molecules increases with an increase in temperature.
- Charles’s law states that the volume of a gas is directly proportional to its absolute temperature at constant pressure.
- The density of an object is its mass per unit volume.
- The density of an object will decrease if it is taken to a higher altitude.
- The upthrust or buoyant force acting on an object submerged in a fluid is equal to the weight of the fluid displaced by the object.
- Pascal’s law states that a change in pressure applied to an enclosed fluid is transmitted undiminished to all portions of the fluid.
- Archimedes’ principle states that the buoyant force acting on an object submerged in a fluid is equal to the weight of the object displaced by the fluid.
- Heat is the energy transferred between two objects due to a temperature difference.
- The transfer of heat through a substance by the movement of the substance itself is called convection.
- The transfer of heat through a substance without any movement of the substance is called conduction.
- The transfer of heat through electromagnetic waves is called radiation.
- The process of a liquid changing into a gas at its boiling point throughout the liquid is called boiling.
- The process of a liquid changing into a gas at its surface, even below the boiling point, is called evaporation.
- The change of a substance from a solid to a liquid is called melting.
- The change of a substance from a gas directly to a solid without passing through the liquid state is called deposition.
- The transfer of energy that occurs when molecules collide is called conduction.
- Heat energy flows from an object with a higher temperature to an object with a lower temperature.
- The transfer of heat through a vacuum by electromagnetic waves is radiation.
- A bimetallic strip is used in thermostats because of the different rates of expansion of the two metals.
- When the volume of a gas is doubled at constant temperature, the pressure becomes half of the initial pressure.
- The state of matter with the least kinetic energy and weakest forces between particles is a gas