Flashcards Potential Difference and Power

What terminal of the battery does an electron enter after delivering its energy to a circuit component?

It re-enters via the positive terminal to be resupplied with energy.

What alternative unit equivalence for the volt is derived from the power formula P=IV?

1 volt= 1 watt per ampere (1 V= 1W A^−1).

How is electrical power (P) defined in terms of energy transferred (ΔE) and time (Δt)?

Power is the rate of energy transfer (P= ΔE //Δt ).

What fraction of total power produced by a source is dissipated internally across its internal resistance r in a simple circuit?

Pinternal // Ptotal = (I^2r // Iε) = (Ir/ε) = (r / R + r)

In an electric circuit, what is the primary role of the battery regarding charge carriers?

It acts as an energy source that does work on charge carriers, resupplying them with potential energy.

Why does terminal potential difference decrease as current drawn from a power source increases?

As current I increases, the lost volts (Ir) across internal resistance increase, leaving less potential difference (V=ε−Ir) for the external circuit.

How does doubling the current through a constant resistor affect the power dissipated by it?

The power quadruples (4×), because P∝ I^2 when resistance R is constant.

What formula gives potential difference (V) in terms of power (P) and current (I)?

V= P // I

How is potential difference (V) defined in terms of work done and charge?

Potential difference is defined as the work done (or energy transfer) per unit charge passing through a component (V=W/Q).

How is the current drawn by a 230 V,800 W appliance calculated?

≈3.48 A

State Ohm's Law

In ohmic conductors, the current that flows through the conductors is directly proportional to the potential difference across the conductors at constant temperature.

What expression gives work done (W) in terms of current (I), potential difference (V), and time (Δt)?

W= IVΔt

By combining P=IV and I=V/R, what is the expression for electrical power in terms of potential difference and resistance?

P= V^2 / R

Under what condition is the terminal potential difference across a cell exactly equal to its electromotive force?

When no current is drawn from the cell (I=0), such as in an open circuit.

In an electrical heater, what equation calculates thermal energy output in terms of resistance R, current I, and time t?

E= I^2Rt

How is terminal potential difference (V) expressed in terms of emf (ε), current (I), and internal resistance (r)?

V= ε−Ir

How is energy efficiency of an electrical supply delivering useful power Pout from total power Ptotal expressed?

Efficiency = (Pout / Ptotal) = (IV / Iε) = (V / ε)

How is electric current (I) defined in terms of charge (Q) and time (t)?

Electric current is the rate of flow of charge (I=ΔQ / Δt).

What physical feature of a chemical cell causes internal resistance?

Resistance to the movement of charge carriers through the internal chemicals and electrolyte of the cell.

What kinetic energy equation applies to an electron accelerated from rest across a potential difference V?

eV= 1/2(m)(v)^2

What opposing force must electrons overcome when moving through the coil of a spinning electric motor?

An opposing electromagnetic force exerted on the moving electrons due to the motor's magnetic field.

What formula calculates the work done (W) when charge Q flows through a potential difference V?

W= QV

Into what main energy form is work done on a vibrating loudspeaker coil transferred?

Sound energy.

In a fluorescent tube, what mechanism allows accelerated electrons to excite gas atoms?

Inelastic collisions between free electrons and orbital electrons of gas atoms, transferring energy to them.

What formula links energy transferred (ΔE), potential difference (V), current (I), and time interval (Δt)?

ΔE= VIΔt

How is electrical resistance (R) defined mathematically?

R = V / I

What equation expresses charge flow (Q) in terms of steady current (I) and time interval (Δt)?

Q = IΔt

What is the total energy transferred when a charge of 3 C moves across a potential difference of 12 V?

36J

By combining P=IV and V=IR, what is the expression for electrical power in terms of current and resistance?

P = I^2R

What is the effect on the rate of heat generation in a component if pd V across a fixed resistance R is halved?

The power reduces to one-quarter (1/4×) of its original value, since P ∝ V^2.

What factor is used to convert energy values from electronvolts (eV) to joules (J)?

Multiply by the elementary charge e (1.60×10^−19 J eV^−1).

What formula gives the maximum energy a battery can deliver if it has emf ε and total charge capacity Qmax?

Emax= Qmaxε

What is the potential difference across a component if 30 J of work is done when 5 C of charge flows through it?

6V

What happens energy-wise to an electron as it passes through a battery in a complete circuit?

It gains a fixed amount of electrical energy from the chemical store of the battery.

How is useful power delivered to external circuit components calculated using terminal pd (V) and current (I)?

Pout= IV

Under what condition is maximum power transferred from a supply with internal resistance r to an external load resistor R?

When the external load resistance equals the internal resistance (R = r).

What equation calculates energy transfer (ΔE) from power rating (P) and operating duration (t)?

ΔE= Pt

What formula gives the total electrical energy (E) produced when charge Q passes through a source of emf ε?

E = Qε

Which equations link electromotive force (ε), current (I), load resistance (R), and internal resistance (r)?

1. ε= I(R+r)

2. (ε =IR+Ir)

Why is the total electrical energy produced by a battery not always completely delivered to the external circuit?

Some energy is dissipated internally within the battery due to its internal resistance.

What force opposes the movement of electrons through the coil of a loudspeaker?

The opposing magnetic force exerted on the electrons by the loudspeaker magnet.

Why are 1 J C^−1 and 1 W A^−1 dimensional equivalents for the volt?

Since 1 W=1 J s^−1 and 1 A=1 C s^−1, dividing gives 1 J C^-1

If a potential difference across a component is 4 V, how much power is delivered per ampere of current?

4 W per ampere (4 W A^−1).

How does doubling the potential difference across a constant resistor affect the power dissipated by it?

The power quadruples (4×), because P ∝ V^2 when resistance R is constant.

What formula gives current (I) in terms of power (P) and potential difference (V)?

I = P / V

How is electromotive force (emf, ε) defined for an electrical source?

Electromotive force is defined as the total electrical energy produced per unit charge passing through the source (ε= E / Q).

What is the key conceptual difference between electromotive force (emf) and potential difference (pd)?

Emf measures energy transferred into electrical energy per unit charge by a source, whereas pd measures electrical energy transferred into other forms per unit charge by a component.

How is P=IV derived from the definitions of power, work done, and charge flow?

Since P= W/Δt and W= IVΔt, substituting gives P= IVΔt/Δt=IV.

How is 1 watt defined in fundamental SI units of energy and time?

1 W = 1 J s^−1 (one joule per second).

What is meant by 'lost volts' (Vlost) in a power supply circuit?

The potential difference dropped across the internal resistance of the source (Vlost = Ir).

In an electric motor turning at a constant speed, why does its kinetic energy remain constant despite continuous work being done on it?

The work done by the charge carriers equals the energy transferred to the external load and surroundings, keeping kinetic energy constant.

In a forward-biased semiconductor diode, what happens to the energy transferred by charge carriers passing through it?

Energy is used to overcome the internal barrier potential and is released as heat or photons (in LEDs).

At the atomic level, how is electrical work converted into thermal energy in a resistor?

Charge carriers repeatedly collide with lattice atoms in the resistor, transferring kinetic energy to them and causing the atoms to vibrate with greater amplitude.

How does energy conservation apply per coulomb of charge in a complete circuit with non-zero internal resistance?

The total energy supplied per coulomb by the source (emf, ε) equals the sum of energy lost per coulomb across external components (V) and internal resistance (Ir)

What is the SI unit of potential difference, and how is it defined in terms of fundamental SI units?

The unit is the volt (V), where 1 volt is equal to 1 joule per coulomb (1 V = 1 J C^−1).