PHYS204
What is ac?
- Alternating current - Charge moves first one way then the opposite way, changing direction from moment to moment
What is q=CV?
- Charge on each capacitor plate § q - charge on each plate § C - capacitance § V - potential between plates
What is F=k (|q_1 ||q_2 |)/r^2?
- Coulomb's Law - F - Electrostatic force - Newton (N) - k - proportionality constant - N∙m^2/C^2 - q1 and q2 - point charges - Coulomb (C) - r - distance between point charges - meter (m)
What is κ=E_0/E?
- Dielectric constant □ κ - dielectric constant □ E_0 - field magnitude without dielectric □ E - field magnitude inside dielectric
What is a dc?
- Direct current - Charge moves around a circuit in the same direction at all times
What is E ⃗=F ⃗/q_0?
- Electric field - E ⃗ - Electric field - Newton per Coulomb (N/C) - Direction is same as Force F ⃗ on a positive test charge - F ⃗ - Force - Newton (N) - q_0 - Charge of test charge - Coulomb (C)
What is E=−∆V/∆s?
- Electric field between capacitor plates / potential gradient § ∆V - potential difference § ∆s - displacement / component parallel to electric field of distance between 2 points § SI Unit: volts per meter § Gives only the component of the electric field along the displacement, not the perpendicular component
What is Energy=1/2 qV=1/2 CV^2=q^2/2C? Energy density=Energy/Volume=1/2 κϵ_0 E^2?
- Energy stored in a capacitor ○ Energy=1/2 qV=1/2 CV^2=q^2/2C § q - charge § V - potential § C - capacitance ○ Energy density=Energy/Volume=1/2 κϵ_0 E^2 § κ - dielectric constant § ϵ_0 - permittivity of free space § E - electric field
What is ∑▒〖(Ecosϕ)ΔA=Q/ϵ_0 ?
- Gauss' Law § Q - net charge § E - electric field § Φ - the angle between the electric field and the normal § ∆A - areas of tiny sections of Gaussian surface § ϵ_0 −permittivity of free space § SI Unit: N∙m^2/C
What is V=IR?
- Ohm's Law - V - potential - I - current - R - resistance
What is E=q/(ϵ_0 A)=σ/ϵ_0?
- Parallel plate capacitor - E - electric field - q - charge` - ϵ_0 −permittivity of free space - σ −charge density or charge per unit area - A - area
What is ∆V=∆(EPE)/q_0 =〖−W〗_AB/q_0?
- Potential difference § ∆V=V_B−V_A ; Potential difference § ∆(EPE)=EPE_B−EPE_A ; Change in electric potential energy
What is ρ? What is its si unit?
- Resistivity (proportionality constant) - SI Unit: ohms∙meter (Ω∙m)
What is V=EPE/q_0? What is the SI Unit?
- The electric potential aka potential § V - electric potential § EPE - electric potential energy of charge § q_0 - charge § SI Unit: joule/coulomb=volt (V)
What is the right hand rule 1?
- thumb - velocity or current - 4 fingers - magnetic field - palm - force (positive)
A positive charge accelerates from a region of 1.___ toward a region of 2.___. A negative charge accelerates from a region of 3.___ toward a region of 4.___
1. Higher electric potential 2. lower electric potential 3. lower potential 4. higher potential
How is the positive and negative terminal represented in a diagram?
2 bars; shorter is negative, longer is positive
What is a solenoid?
A long coil of wire in the shape of a helix
What kind of wave is the electromagnetic wave?
A transverse wave because the electric and magnetic fields are both perpendicular to the direction in which the wave travels
What is a resistor?
A wire or an electrical device that offers resistance to the flow of charges
What is ∑▒〖B_(||) ∆l=μ_0 I 〗?
Ampere's Law; for any current geometry that produces a magnetic field that does not change in time □ ∆l - a small segment of length along a closed path of arbitrary shape around the current □ B_(||) - the component of the magnetic field parallel to ∆l □ I - the net current passing through the surface bounded by the path □ μ_0 - permeability of free space
What charge does an object with a surplus of electrons? What about an object that lack electrons?
An object with a surplus of electrons are negatively charged while an object lacking electrons are positively charged
What is P ̅=I_rms V_rms=I_rms^2 R=(V_rms^2)/R?
Average power § P ̅ - average power § I_rms - root-mean-square current § V_rms - root-mean-square voltage
What is q=q_0 [1−e^(−t/RC) ]?
Capacitor charging
What is q=q_0 e^(−t/RC)?
Capacitor discharging
What is an electric dipole?
Consists of two separated point charges that have the same magnitude but opposite signs
What is the SI unit for measuring the magnitude of an electric charge?
Coulomb (C)
What is I=∆q/∆t? What is its SI unit
Current □ ∆q - amount of charge □ ∆t - time □ Rate of flow must be constant. If it is not constant, then this equation gives the average current □ SI Unit: Ampere (A) = Coulomb per second (C/s)
What is the direction of electric field lines? What relationship do the number of lines have with the magnitude of the electric field?
Directed away from positive charges and toward negative charges. Always begin on a positive charge and end on a negative charge and do not start or stop in midspace. Furthermore, the number of lines leaving a positive charge or entering a negative charge is proportional to the magnitude of the charge
What is the Law of Conservation of Electric Charge?
During any process, the net electric charge of an isolated system remains constant. No electrons or protons are created or destroyed.
What is EA or ∑▒(Ecosϕ)ΔA? What is the maximum flux? How does the electric field pass through the surface at maximum flux? minimum flux? tilted surface?
EA (maximum flux) ∑▒(Ecosϕ)ΔA - E - electric field - A - area of the surface - Φ - the angle between the electric field and the normal At maximum flux, the electric field passes through the surface perpendicularly. At a tilted surface, only the perpendicular component of the electric field passes through the surface. At minimum flux, the electric field does not pass through the surface
What is P=IV=I^2 R=V^2/R? What is its SI unit?
Electric power § P - electric power § I - current § V - voltage between points § R - resistance § SI Unit: watt (W)
What is emf?
Electromotive force - the maximum potential difference
What is R_S?
Equivalent resistance
Describe the electrostatic forces between objects
Forces between objects, whether attractive or repulsive, are equal in magnitude and are opposite in direction
What happens if the current in one device is interrupted in a series wiring?
If current in one device is interrupted, the current in other devices is also interrupted
What happens if the current in one device is interrupted in a parallel wiring?
If current in one device is interrupted, the current in other devices is not interrupted
How is the internal resistance connected with external resistance?
In series
What magnitude of the electric field can a gaussian surface have?
It can vary from point to point, it is not necessarily constant
What relationship does distance have with the magnitude of the electric field?
It is stronger the closer to the charge
How is the electric field between capacitor plates?
It is the same everywhere
How do like and unlike charges interact with one another?
Like charges repel and unlike charges attract each other (with a force exerted)
How do magnet poles interact with each other?
Like poles repel, unlike poles attract
What is B=(μ_0 I)/2πr?
Magnetic field of a current carrying wire □ μ_0 - permeability of free space □ I - current □ r - radial distance
What is the relationship between electrons and an object's mass?
More electrons means more mass
What is V_rms=I_rms R?
Ohm's law
What is C_P=C_1+C_2+C_3+...? What's important about it?
Parallel capacitors - When capacitors are connected in parallel, the voltages are the same, but the capacitors contain different charges - The charge of the equivalent capacitance is the sum of all charges
What is 1/R_P =1/R_1 +1/R_2 +1/R_3 +..?
Parallel resistors
What is μ_0?
Permeability of free space
In the loop of wire, what is the direction of the magnetic field. How is the direction found?
Perpendicular to the plane of the loop. The direction can be found with RHR 2.
What is V=kq/r? When is it positive and when is it negative?
Potential of a point charge § V - potential at a distance r from a point charge differs from the potential at an infinite distance away; a potential difference with the arbitrary assumption that the potential at infinity is zero § k - proportionality constant § q - point charge § r - distance - Positive when charge is positive and negative when charge is negative
What is R=ρ(L/A)?
Resistance § R - resistance § ρ - resistivity (proportionality constant) § L - length of material § A - cross-sectional area in material
What is R=R_0 [1+α(T−T_0 )]?
Resistance depending on temperature □ R - resistance at temperature T □ R_0 - resistance at temperature T_0 □ α - temperature coefficient of resistivity
What is ρ=ρ_0 [1+α(T−T_0 )]?
Resistivity depending on temperature □ ρ - resistivity at temperature T □ ρ_0 - resistivity at temperature T_0 □ α - temperature coefficient of resistivity
What's an RC Circuit?
Resistor-Capacitor circuit - A circuit that contains both a resistor and capacitor
What are semiconductors?
Semiconductors - at ordinary temperatures, these objects are poor conductors of electricity; as temperature rises, electrons break free and move freely through the material
What is 1/C_S =1/C_1 +1/C_2 +1/C_3 +...? What's important about it?
Series capacitors - When capacitors are connected in series, the voltages are different, but the charges are the same
What is R_S=R_1+R_2+R_3+ ..?
Series resistors
What is the direction of the magnetic field?
Starts from the north pole and ends on the south pole
What is C=(κϵ_0 A)/d?
The Capacitance between parallel plate capacitors filled with a dielectric § C - capacitance § κ - dielectric constant § ϵ_0 - permittivity of free space § A - area of each plate § d - separation between plates
What is parallel wiring?
The devices are connected in such a way that the same voltage is applied across each device
What is a series wiring?
The devices are connected in such a way that there is the same electric current through each device
Why do some substances conduct electrical charges well?
The electrons in the outer orbits experience a weaker force of attraction; hence, the electrons detach from its parent atom and moves freely.
What is an electric current?
The flow of charge crossing perpendicularly of an imaginary surface inside a wire
What is an electric / electrostatic force and what does it do?
The force charges exert on one another, and it contributes to the external force that acts on the object, possibly altering its motion
What is B=F/|q_0 |(vsinθ)? What is its SI Unit?
The magnetic field § B - magnitude of the magnetic field at any point in space § F - magnitude of the magnetic force on a test charge § 〖|q〗_0 | - magnitude of the test charge § v - magnitude of the charge's velocity § θ - angle with the direction of the magnetic field § SI Unit: (newton∙second)/(coulomb∙meter)=tesla (T)
What is B=N (μ_0 I)/2R?
The magnetic field at the center of a circular loop □ B - Magnetic field □ N - number of loops □ μ_0 - permeability of free space □ I - Current □ R - radius
What is B=μ_0 nI?
The magnetic field at the interior of a solenoid □ n - the number of turns per unit length □ I - current □ μ_0 - permeability of free space □ B - magnetic field
What is the magnetic field around a solenoid?
The magnetic field outside the solenoid is not constant and is much weaker than the interior field
What is F=ILBsinθ?
The magnetic force on a current-carrying wire § F - Magnetic force § I - Current § B - Magnetic field § Θ - Degrees between the Magnetic field and current
What are thermal conductors? electrical conductors?
Thermal conductors are objects which conduct heat rapidly. Electrical conductors are substances that readily conduct electric charge.
What are thermal insulators? Electrical insulators?
Thermal insulators are substances which conduct heat poorly. Electrical insulators are substances that conduct electric charge poorly.
How are the electric and magnetic fields in electromagnetic waves directed?
They are perpendicular to each other
How do electrons travel from one object to another?
Through contact or induction
What is τ=NIA(Bsinϕ)?
Torque on a current-carrying loop § τ - Torque § N - Number of loops § I - Current § A - Area § B - Magnetic field § Φ - Angle between normal to the plane of the loop and direction of the magnetic field
How is the potential obtained when two or more charges are present?
When two or more charges are present, the potential due to all the charges is obtained by adding together the individual potentials
Does a current-carrying wire produce a magnetic field of its own? How is the direction found?
Yes. Direction is found with Right hand rule 2. - 4 fingers - magnetic field - thumb - current
What is charge distrubution?
a collection of charges spread out over a region
What is a gaussian surface?
an imaginary closed surface that can have any arbitrary shape but must be closed
What is an electrically neutral object
an object that carries no net charge
What is the si unit of capacitance?
coulomb / volt = farad (F)
What is the radiation field in an electromagnetic wave?
electric and magnetic fields forming a wave that arise at larger distances from the source
What other name can the electric field called?
lines of force
Does the direction of electric field lines have to be perpendicular to the gaussian surface?
no
What is k in equations?
proportionality constant
What is the near field in an electromagnetic wave?
the electric and magnetic fields that exist mainly near its source
What is the anode?
the negative terminal of a battery
What does it mean if an electric force is conservative?
the path the the test charge moves from A to B does not matter
What is a cathode?
the positive terminal of a battery
What is charging by contact?
the process of giving one object a net electric charge by placing it in contact with another object that is already charged
What is charging by induction?
the process of giving one object a net electric charge without touching the object to a second charged object
What are the conditions for a charge to experience a magnetic force?
§ The charge must be moving, because no magnetic force acts on a stationary charge § The velocity of the moving charge must have a component that is perpendicular to the direction of the magnetic field □ If the charge moves perpendicular to the magnetic field, it experiences the maximum possible force; if it moves parallel, it experiences no magnetic force
What Kirchhoff's Rules?
• Junction rule ○ The sum of the magnitudes of the currents directed into a junction equals the sum of the magnitudes of the currents directed out of the junction • Loop rule ○ Around any closed-circuit loop, the sum of the potential drops equals the sum of the potential rises § The choice of direction is arbitrary; if incorrect, I will be negative
What is an equipotential surface? What happens when a charge moves on an equipotential surface? What direction is the electric field with respect to the equipotential surface?
○ A surface on which the electric potential is the same everywhere ○ The net electric force does no work as a charge moves on an equipotential surface ○ The electric field created by any charge or group of charges is everywhere perpendicular to the associated equipotential surfaces and points in the direction of decreasing potential
What is a dielectric? What does it do?
○ An insulating material commonly filling the region between conductors or plates ○ Increases the capacitance when placed between plates in capacitor
What are some important information regarding conductors and electric fields?
○ At equilibrium under electrostatic conditions, any excess charge resides on the surface of a conductor ○ At equilibrium under electrostatic conditions, the electric field is zero at any point within a conducting material ○ The conductor shields any charge within it from electric fields created outside the conductor ○ The electric field just outside the surface of a conductor is perpendicular to the surface at equilibrium under electrostatic conditions
What does a capacitor consist of? What is important about each capacitor plate?
○ Consists of two conductors of any shape placed near one another without touching ○ Each capacitor plate carries a charge of the same magnitude, one positive and one negative
I_rms=I_0/√2. Determine the equation's components.
○ I_0 - peak current
V_rms=V_0/√2. Determine the equation's components.
○ V_0 - peak voltage
W_AB=EPE_A−EPE_B
○ W_AB - work ○ EPE_A - electric potential energy at point A ○ EPE_B - electric potential energy at point B
