physics

A compass needle itself is a small bar magnet. All external / applied magnetic field points in the direction of the compass's north pole.

T

A current-carrying wire can generate a magnetic field. The strength of this magnetic field can be determined by Biot-Savart Law, and is proportional to current, I but inversely proportional to the distance from the wire, d. The direction of this magnetic field can be determined by the right-hand rule.

T

A light bulb is connected to a battery and is glowing. The light bulb goes out when a wire is added across the light bulb (wire becomes parallel to the bulb and the battery). From this observation, we can say that, The wire has no resistance, and hence the potential difference across the wire and the light bulb becomes zero. Therefore, no current passing through the light bulb.

T

A moving charge can produce a magnetic field. The strength and direction of such a magnetic field can be determined by the Biot-Savart law.

T

According to Bio-Savart law, the direction of the magnetic field generated by a moving positive charge is perpendicular to the plane containing the direction of the moving charge and the point, P where you are interested in finding the magnetic field. Such a direction will reversed for a negative charge.

T

All area vectors are normal vectors, i.e., perpendicular to the surface; and point outward from a closed surface. The angle between the area vector and the electric field vector will decide if it is a positive or negative flux.

T

Ampère's Law states that the line integral of the magnetic field around a closed path (imaginary loop) is proportional to the current passing through the loop

T

An electric dipole is form by two equal but opposite charges separated by a small gap. The dipole moment, p=qs pointing from the negative to positive charge

T

An electrical potential difference can be created by separating different types of charges at opposite locations.

T

At a point located in the middle of two like charges, the net electric field is zero. At a point located in the middle of two unlike charges, the net electric field is non-zero.

T

Based on Biot-Savart Law, a circular current loop will generate a magnetic field at the center and the loop behaves like a magnet and is called an electromagnet. The strength of the magnetic field is proportional to the current I, and inversely proportional to the radius of the loop. The direction of the magnetic field can be determined by the right-hand rule.

T

Bulbs rated at 25 W and 60 W are connected in series across a 120 V source. The 25W bulb is brighter because it receives the same current, I, as of the 60W bulb, and it has a higher resistance, R.

T

Capacitance will increase when a dielectric is inserted into a parallel-plate capacitor that was initially filled with air or vacuum. This is because dielectric constants are always larger than 1.

T

Changing the location of the ground point in a circuit will not change the circuit's behavior, i.e., will not change the potential difference across all electrical elements (resistors, light bulbs, etc.).

T

Charging a RC circuit will increase the amount of charge and potential difference on the capacitor. Therefore, the potential difference across the resistor will decrease s suggested by the Loop's law, and the current flow through the resistor will decrease.

T

Conservation of energy applied when the electric force is the only force being applied to move a charge.

T

Current flow in a conducting wire will produce a magnetic field. Therefore, a compass needle near the wire will point along the direction of this external magnetic field.

T

Current is caused by an electric field exerting forces on charge carriers. The current density depends linearly on the electric field strength. The current density depends on the material's conductivity.

T

Discharging a RC circuit will remove the amount of charge on the capacitor, reducing the potential difference across the capacitor, and the resistor. The current flow through the resistor will be decreased with time. The time constant, RC, is defined as the time taken to reduce the charge or current to e-1 of the initial values.

T

Drift velocity, vd is higher when the diameter of the current-carrying wire is smaller.

T

Electric field lines for a dipole are drawn such that Lines originate on positive charge and terminate on negative charge Lines are closer together and the electric field strength is largest between the charges the tangent to a field line at a point is in the direction of the electric field at that point. Lines never cross

T

Electric field strength, E is higher when the diameter of the current-carrying wire is smaller.

T

Electric flux is directly proportional to the net charge enclosed within a closed Gaussian surface.

T

Electric force is a conservative force. Work done by the electric force is independent of the path followed.

T

Electron current is different from conventional current, I. Current I is defined as the number of charges per second that pass through a wire or a conductor. I is flow in the opposite direction as ie.

T

Electron current, i_e is defined as the number of electrons per second that pass through a cross-section of a wire or a conductor. Electron current is conserved at all points in a current-carrying wire.

T

Energy storage is maximum if two capacitors are connected in parallel to the batteries.

T

For a charged hollow conductor the electric field inside the conductor is zero.

T

For a charged hollow conductor, opposite charges can be located on the inner and outer surface. This can happen only when charge polarization is produced by another charged object.

T

For a charged object that is very far away from the point of observation, P, we can treat the object as a point charge.

T

For a closed surface with no enclosed net charges, and located within a uniform electric field (parallel-plate capacitor), the total flux enters into the closed surface is equal to the total flux exit from the closed surface. Therefore the net flux through the closed surface is zero and there is zero net charge inside the enclosed surface.

T

For a negative charge such as an electron, its acceleration, a is in the opposite direction of the uniform electric field and is proportional to the charge to mass ratio

T

For a neutral hollow conductor, opposite charges can be located on the inner and outer surface. This can happen only when charge polarization is produced by another charged object.

T

For a neutral hollow conductor, the electric field inside the conductor is zero.

T

For a point charge, the equipotential surfaces are concentric circles, and The electric field is everywhere perpendicular to the equipotential surfaces. The electric field points in the direction of decreasing potential. The electric field strength is inversely proportional to the spacing between equipotential surfaces.

T

For a positive charge, q; its acceleration, a is in the same direction of the uniform electric field and is proportional to the mass to charge ratio.

T

For a resistor connected to an ideal battery, The potential difference across the resistor is equal to the emf supplied by the battery. The potential difference creates an electric field inside the resistor. Current flow from the positive terminal of the battery to the negative terminal through the resistor.

T

For a very long charge rod, we may treat it as an infinite line of charge, such that the electric field from point P, at a distance of r away is inversely proportional to r.

T

For conductors in electrostatic equilibrium, the electric field, E inside the conductor is zero. This means the electric potential inside the conductors is the same everywhere.

T

For the above-mentioned resistor, we can say that it is ohmic when The resistance is constant, The current will linearly increase with the increase of the applied potential difference.

T

If a wire is connected between two points that initially are at different electric potentials, the wire quickly makes the electric potential difference between those points equal to zero. Any circuit elements between the two points so connected are said to be shorted out.

T

If we know the electric potential throughout a region of space, we also know the electric potential energy of any charged particle that enters that region: U=qv

T

Impedance matching (r=R) is a condition where maximum power transfer is obtained between the power source (says a battery with internal resistance, r) and the power load (says a light bulb/resistor with a resistance, R).

T

Kirchhoff's Junction Law states that the total current, I(in) entering to a junction is the same as the total current, I(out) that exit from the junction.

T

Kirchhoff's loop law states that the total potential difference across all electrical elements connected in a closed loop is equal to zero. This is true when evaluating the potential differences around the loop in the same direction (best along the direction of the current flow).

T

Linear charge density is charge per unit length, surface charge density is charge per unit area, and volume charge density is charge per unit volume.

T

Magnetic fields generated by two identical and adjacent current loops superimpose and follow the principle of superposition. These fields will build up and the loops will attract if the loops carrying currents in the same direction. Otherwise, the magnetic fields will be canceled and the loops repel each other.

T

Magnets have two poles: north and south. Magnetism is a long-range force. Unlike poles attract; like poles repel.

T

Ohm's Law states that current flow, I across an electrical element (resistor, light bulb, etc.) is directly proportional to the potential difference across the element. current flow, I across an electrical element (resistor, light bulb, etc.) is inversely proportional to the resistance, R of the element.

T

Outside a spherically symmetric charge distribution, the electric potential is identical to that of a point charge at the center. This is true for spherical shell charges and uniformly distributed spherical charges.

T

Parallel capacitors have the same electric potential difference across their plates. The equilibrium capacitance is equal to the sum of the individual capacitance.

T

RC, the product of resistance and capacitance, has dimensions of time. RC is referred to as the time constant for a circuit consists of one or more resistors and capacitors.

T

Removing a light bulb (or another electrical element) between points a and b results in an open circuit - a non-conducting gap with infinite resistance. The current ceases to flow. The potential difference between points a and b is the emf of the source.

T

Right-Hand Rule can be used to determine the direction of a magnetic field produced by a current-carrying wire as follows, Grab the wire with your right hand with your thumb in the direction of the current. Stretch and place your four other fingers at the location where you wanted to find out the direction of the magnetic field. Your four other fingers curl in the direction of the magnetic field.

T

Series capacitors have the same charge on their plates. The inverse of the equilibrium capacitance is equal to the sum of the individual inversed capacitance.

T

Since the emf is constant, the power supply by a battery will depend on the current flow, I, which is decided by the resistance, R of the circuit (the load). Therefore, the power supply from a battery will changed when connected to different loads (resistors).

T

Static charges or charged object will not produce a magnetic field.

T

The change in electric potential energy is equal to the work done when moving the charged particle.

T

The electric field at point P, at a distance d away from a charged plate is independent of the value d, if the dimension of the plate is very much larger than d.

T

The electric field inside a conductor is always zero.

T

The electric field inside a parallel-plate capacitor is double of the electric field of a uniform infinite plane charge. The electric field outside the parallel-plate capacitor is zero.

T

The electric field lines are always perpendicular to the equipotential surfaces, and points from high to low electric potential.

T

The electric field of a point charge is inversely proportional to the square of the distance, r between the source charge and the point of measurement, P. However, the electric field of a uniform infinite line charge is inversely proportional to the distance, r between the source charge and the point of measurement, P.

T

The electric field of a spherical volume charge is the same as that of a point charge.

T

The electric field of a uniform infinite plane charge is the same as measured from any distance, r between the plane and the point of measurement, P.

T

The electric field, Es is equal to the negative value of the gradient (slope) of a graph of electric potential, V versus distance, S:Es=-dV/ds

T

The electric flux through a closed surface is proportional to the net electric charge inside the surface, regardless of the shape of the closed surface.

T

The electric flux through a surface depends on the magnitude of the electric field (E), the area of the surface (A), and the angle between the electric field vector and area vector.

T

The electric potential energy for a dipole is least when the dipole moment points in the same direction as the electric field.

T

The electric potential energy is least where the oppositely charged particles are closest.

T

The electric potential energy, U, is inversely proportional to the distance from a charge.

T

The electric potential energy, U, is inversely proportional to the square of the distance from a charge.

T

The electric potential of a ground point is equal to that of the earth and is assigned the value of zero. Adding a ground point to a circuit allows us to find the electric potential at any point in the circuit.

T

The electric potential of a group of point charges obeys the superposition principle, i.e., equal to the sum of the electric potential of every individual point charges.

T

The electric potential of a point charge, V is inversely proportional to the distance, r from the point charge, and only depends on the source charge, q. Therefore, the equipotential surfaces of the point charge are concentric circles surrounding the charge.

T

The electric potential within a parallel plate capacitor is, V=Es , where E is the electric field, and S is the distance from the negative plate. Because of this linear relation between V and S, the electric potential within the capacitor can be represented by a series of equipotential planes that are parallel to the capacitor plates.

T

The equivalent resistance for a group of parallel resistors is less than the resistance of any resistor in the group. The equivalent resistance for a group of series resistors is more than the resistance of any resistor in the group.

T

The magnitude of the magnetic dipole moment, of a current loop with current I and area A is the product of IA. The direction of the magnetic dipole moment can be determined by the right-hand rule and pointing to the north pole. The strength of the magnetic field generated by a current loop is proportional to the magnitude of the magnetic dipole moment, and inversely proportional to z3, where z is the distance from the loop along the direction of the magnetic field.

T

The net field created by a group of charges is the vector sum of fields created by individual charges. This is based on the principle of superposition.

T

The potential difference across a battery when "travel" from the negative to the positive potential is considered as a positive value. The reversed is true.

T

The potential difference across a resistor when "travel" along the direction of current flow (i.e., from the end connected to the positive terminal of a battery) is considered as a negative value (a potential drop). The reversed is true.

T

The principle of superposition applied for magnetic fields, for examples, A magnetic field strength can be canceled by applying another magnetic field in the same space with the same strength but opposite in direction. A magnetic field strength can be doubled by applying another magnetic field in the same space with the same strength and same direction.

T

The principle of superposition can be used to find out the net electric field at a point P from a group of charged objects.

T

The real battery is a source of emf in series with an internal resistor, r. The potential difference across the real battery is lower than the emf due to a potential drop across the internal resistor.

T

The recommended strategy to perform analysis on a circuit with multiple resistors is, (a) Step by step, reduce the number of resistors by repacing resistors that are connected in parallel (or in series) with an equivalent resistor. (b) Repeat (a) until you have simplified the circuit into a single loop. (c) Next, apply Kirchhoff's loop's law to find out the current and potential difference for the resistor(s) in the loop. (d) Then, analyze the circuits that you have obtained in the processes (a) and (b) one at a time follow the backward order. Find the current and potential differences for all resistors by the following facts: (i) current is the same through all resistors in series (ii) potential difference is the same for all parallel resisto

T

The resistance of copper wires, says with a diameter of 1mm, is very small as compared to the resistances of resistors of 1 ohm to 1 megaohm. Therefore, we can use copper wires as ideal wires, to connect electrical circuits without considering their resistance.

T

There is no net force on an electric dipole in a uniform electric field. Therefore, no linear motion on the dipole. There is, however, a tendency for the electric dipole to rotate as indicated by a non-zero torque.

T

Two light bulbs (or resistors) in parallel have the same potential difference across them.

T

Two light bulbs (or resistors) in series have the same current through them. Since the current is common for these light bulbs/resistors, the power dissipation of the light bulbs/resistors is P=I^2*R

T

We can use the principle of superposition to find a point P where the net electric field from a group of point charges becomes zero. In this case, vector summation of all the electric fields generated by all individual charges on point P must become zero

T

We can use the principle of superposition to find a point P where the net electric field from two or more charged objects becomes zero. In this case, vector summation of all the electric fields generated by all individual charged objects on point P must become zero.

T

When the electric field is tangent to the surface, the electric flux through the surface is zero.

T

When the electric potential energy is minimum, the kinetic energy is maximum, and vice versa.

T

When the potential difference across a parallel-plate capacitor is doubled, the capacitance remains the same

T

Coulomb's law indicates that forces on two charged particles are (i) acting along the line joining the two particles, (ii) equal in magnitude and opposite in direction.

True

Electric Field Lines are drawn so that : the tangent to a field line at a point is in the direction of the electric field at that point. they are closer together where the electric field strength is larger they never cross

True

For a negative charge, the direction of electric force is opposite to the direction of electric field. For a positive charge, the direction of electric force is the same as the direction of electric field

True

Forces on two charges are repulsive for two like charges and attractive for two opposite charges.

True

The electric field is (i) a physical quantity that can be felt by a charge at all points in space, (ii) created by the source charge but the source charge does not feel it own field, (iii) can be sense by a probe charge but can not be changed by a probe charge.

True

The total electric force on a charged particle can be calculated by adding all individual forces imposed on the particle by all surrounding charges based on the principle of superposition.

True