Physics 2 Second Test

electricity is made up of ________ particles; what kind?

charged particles; protons (positive) and electrons (negative)

a neutral object will have equal numbers of

protons and neutrons

protons and electrons have charges of equal MAGNITUDE:

|q|= 1.6×10^-19C

charge is always

conserved; can be transferred from one object to another but total amount of charge is constant

conductors

substances that allow for free motion for electrons; may be some loss of KE

examples of conductors

metal and salt water

superconductors

substances that allow for free motion of electrons without any loss of energy

insulators

substances that inhibit the free motion of electrons

examples of insulators

distilled water and gases

two ways an object can be charged

by contact or induction

charging by contact

a charged object directly touches another object and transfers charge to it

charging by induction

no direct contact; a charged object is brought nearby a neutral object; the charges on the neutral object separate and the side closest to the charged object becomes the opposite charge of it and the other end of the object becomes the same charge of it

4 fundamental forces in the universe (in order of strength)

SEWG strong force, electromagnetic force, weak force and gravitational force

strong force

binds quarks together to form protons and neutrons and holds the nucleus of the atom together

electromagnetic force

force between charged particles

weak force 

important for radioactive decay and nuclear processes

gravitational force

force between masses

gravity and electromagnetism similarities

both are mutual forces (equal and opposite reaction) and have inverse square relationships

gravitational force differences

based on masses; relatively weak; operates over large distances; attractive; always positive

electromagnetic force differences

based on charges of objects; relatively strong; operates over short distances; attractive or repulsive; positive (repel) or negative (attract)

Coulomb’s Law

force between two electrostatic charges; F_E=kq₁q₂/r²

Gravitational Force formula

F_G=Gm₁m₂/r²

do field forces require contact to cause motion?

no

Q (point charge) vs q (test charge)

Q causes the electric field, q experiences it AND THE FORCE BETWEEN THEM IS THE SAME

E (Electric field equations)

E=F/q OR E=kQ/r²

positive E fields point; negative E fields point

positive fields point away from point charges; negative fields point towards point charges

Electric Field line 3 rules

1. Field lines exit positive and enter negative charges

2. Larger charges produce greater proportional number of field lines

3. Field lines NEVER cross

The closer field line are together,

the stronger the field is at any point

the direction of the electric field line is ____ to the field line at any point

tangent

when a charged particle accelerates in an electric field, does it gain or lose KE?

gains KE

W=

Fd= change in KE= kQq/r

UE formula (electric potential energy)

-kQq/r

V(electric potential) formula

V= UE/q

1 eV (electron volt)

1.6 × 10^-19 J

Work is done on the charge and is equal to

W=qV or W=qV_AB

V_AB

V_A-V_B

max distance two regions of charge (like parallel plates) can be apart before a spark can be created

V_AB=Ed

equipotential lines

show regions where the potential has the same magnitude; perpendicular to electric field lines, so no work is done

capacitors

store electric charge, usually on two parallel plates(one positive one negative) but are often made into a coil to store greater charge

what’s inside the capacitor and what does it do?

an insulator that keeps the two parallel plates from touching

the amount of charge stored in a capacitor depends on two things:

the voltage of the power source and the physical characteristics of the power source

V UP, Capacitance?

UP

capacitance formula and unit

C=Q/V; unit is 1 F or Farad

parallel plates in capacitors characteristics

equal in Area and identical in materials, separated by a distance with nothing in between them; bigger plates can store more charge

C=ε₀ A/d

is the formula for capacitance in a parallel plate capacitor, where ε0 is the permittivity of free space, A is the area of the plates, and d is the separation distance between them.

dieletric

an insulator allowing for smaller distance between the plates without a discharge in between them which increases capacitance by reducing the electric field strength.

dielectric in capacitor formula

C=kε₀ A/d

Energy of capacitor formulas (Ucap)

Ucap=QV/2 AND Ucap=CV²/2 AND Ucap=Q²/2C

series connection vs parallel connection

direct linkage vs branched linkage

do series have lower or higher capacitance

lower

series capacitance formula

1/C_s=1/C₁ + 1/C₂ + 1/C_n

does each capacitor in series have the same capacitance and voltage

same capacitance in each capacitor, but voltage varies with the individual

parallel capacitance formula

C_p= C₁ +C_n

does each capacitor in parallel have the same capacitance, voltage and current?

voltage (V) stays the same within each capacitor, but charge (Q) and capacitance (C) vary

what is current and what is its formula and what are the units?

the rate at which charge moves; C= Q/t; measured in Amps

why does current come about?

because of a difference in potential between points (voltage)

The voltage creates what that in turn generates what

voltage creates an electric field which in turn generates an electromagnetic fore on the charges

Ohm’s Law

a law stating that electric current (I) is proportional to voltage (V) and inversely proportional to resistance (R)

resistance

anything that impedes current flow; measured in ohm’s

internal resistance

atomic collisions or attractions or devices added to the circuit

Ohm’s Law formula

V=IR

L UP, R ?

R UP

Cross sectional area UP, R?

R DOWN

Resistivity formula

R=p L/A

electrical power

the product of current and voltage

direct current

utilizes only one voltage source and flows in only one direction, so is consant

alternating current

is a type of electrical current that periodically reverses direction and changes voltage levels, typically represented as a sine wave.

what does alternating current allow for with a less loss of potential?

long distance transmission of higher voltages

when resistors are combined in series,

this acts as a longer resistor and the total resistance increases.

when resistors are combined in parallel, 

this acts as if there’s a greater area, and decreases the total resistance

Adding resistors in a series formula

Rtotal = R1 + R2 + RN

Adding resistors in parallel formula

1/Rtotal = 1/R1 + 1/R2 + 1/RN

ammeter is connected in _________ and voltmeter is connected in ___________

series and parallel

electromotive force

the potential difference of a source with no current flowing

internal resistance, r

resistance to a flow of charge within a voltage source itself

terminal voltage formula

difference between the emf and the voltage of the internal resistance, V= E - Ir

when is I positive

when current is flowing from the positive to the negative terminal

when a battery is connected to a load(external) resistance, the load is considered to be in

series with the internal resistance

Ohm’s Law for Terminal Voltage

I= E/R_load+r

Junction Rule

the sum of currents entering a junction must equal the sum of currents exiting a junction

Loop Rule

the sum of the potential (voltage) around a loop must equal zero

When encountering a battery, a potential is positive if you encounter

the negative terminal first

when encountering a resistor, if you’re going in the direction of the current flow, the potential is 

negative

T=RC

is the time constant for an RC circuit, indicating the time it takes for the voltage across a capacitor to charge to approximately 63% of its maximum value

4 elements of an RC circuit

a power source (usually a battery), a resistor, a capacitor, and an open and close switch