Physics

• For refraction at spherical surface, the radius R is positive if the surface is convex toward the object and negative if the surface is concave toward the object.
• The perpendicular distance measured above the principle axis is positive and that below is negative.
• When an object is at 2F of a convex lens, the magnification is -1
• The power of a lens is equal to the reciprocal of the focal length of the lens
• A projector lens produces an enlarged, real image
• A convex lens can be used in a projector when the object is between F and 2F of the lens
• The image formed by a projector is magnified and real
• The image formed on the film of a simple camera is real and diminished
• A magnifying device produces a virtual image that is larger than the object
• Concave lenses always diverge light rays and form only virtual images
• Convex lenses are used in spectacles for long-sighted persons
• Concave lenses are used in spectacles for short-sighted persons
• When the object is between F and 2F of a lens, the image is beyond 2F, real, inverted, and larger than the object
• The focal length of a convex lens is positive and that of a concave lens is negative
• Electric forces are much greater in magnitude than gravitational forces
• The direction of the electric force is always along the line joining the two charges
• If the charges are like charges, the force between them is repulsive and directed outwards
• If the charges are unlike charges, the force between them is attractive and directed inwards
• ε0 = 8.85 x 10^-12 C^2 N^-1 m^-2
• Point charge is a charge without dimension or with dimension much smaller than other dimensions
• Direction of electric field intensity is the same as the electric force acting upon a positive charge, but opposite for a negative charge
• Electric lines of force are close together when electric field intensity is large and far apart when electric field intensity is small
• More highly curved parts indicate greater concentration of charge
• Hollow metal sphere has uniformly distributed charge on the outer surface
• Pointed portion of an object, like a lightning conductor, has highly concentrated charge
• Electric field around a point charge is non-uniform
• Uniform electric field between two oppositely charged parallel plates has parallel electric lines, same direction, equally spaced, and same length
• Electric potential at infinity is considered zero
• Positive charge moves from higher electric potential to lower electric potential
• Negative charge moves from lower electric potential to higher electric potential
• Electric lines are perpendicular to the surface of a charged conductor
• Work done is zero in bringing a charge from one point to another point on an equipotential surface
• Parallel charged plates are two parallel metal plates of the same size and material, carrying charges of equal magnitude and opposite signs, separated by a distance
• Electric potential of the earth is considered zero
• When a positively charged body is connected to the earth, electrons flow from the earth to the sphere at higher potential
• When a negatively charged body is connected to earth, electrons flow from the sphere at lower potential to the earth
• Direction of electric current is opposite to the direction of flow of electrons in a conductor
• Stationary electric charge and the magnetic field do not affect each other
• Moving electric charge or an electric current and the magnetic field have mutual effects between them
• Electric current is the flow of electrons from a place of lower potential to a place of higher potential