EV
Electric vehicles (EVs) are vehicles propelled by electric motors powered by electricity stored in rechargeable batteries, distinguishing them from traditional internal combustion engine vehicles that burn fossil fuels.[1] They encompass battery electric vehicles (BEVs), which operate exclusively on battery power, and plug-in hybrid electric vehicles (PHEVs), which incorporate a battery alongside a gasoline engine for extended range.[2] This configuration enables zero tailpipe emissions during operation, though overall impacts hinge on upstream factors like electricity sourcing and component manufacturing.[3] The origins of EVs trace to the early 19th century, with rudimentary prototypes developed around 1832, followed by commercially viable models in the 1890s that briefly dominated urban markets due to quiet operation and ease of use.[3] Their decline accelerated after 1912 with the advent of affordable electric starters for gasoline cars and abundant cheap oil, relegating EVs to niche status until the 1970s oil crises and subsequent battery innovations spurred revival.[3] The contemporary surge, ignited by lithium-ion battery breakthroughs and vehicles like the 2008 Tesla Roadster, has positioned EVs as a cornerstone of efforts to decarbonize transport, bolstered by subsidies and regulatory mandates in various jurisdictions.[3] By early 2025, EV sales had reached over 4 million units in the first quarter globally, reflecting a 35% year-over-year increase and comprising about one in four new car sales, with China accounting for the majority of volume.[4][5] Lifecycle analyses indicate EVs can achieve 20-70% lower greenhouse gas emissions than comparable gasoline vehicles over their full lifespan, contingent on driving distance exceeding 20,000-50,000 miles and cleaner grid electricity; in coal-dependent regions, net benefits diminish or reverse.[6][7] Advances in battery energy density and production scale have halved costs since 2010, enhancing range to over 300 miles for many models and enabling applications beyond passenger cars, such as buses and trucks.[8] Prominent challenges include the resource-intensive battery supply chain, where mining lithium, cobalt, and nickel entails high water consumption—up to 500,000 gallons per ton of lithium—habitat destruction, and toxic waste, alongside documented ethical issues like child labor in cobalt extraction from the Democratic Republic of Congo.[9][10] Grid reliability strains from charging demands, limited infrastructure in rural areas, and vehicle longevity concerns—batteries degrade after 8-15 years—further complicate scalability, even as recycling rates lag below 5% globally for key minerals.[8] These factors underscore EVs' dependence on technological maturation and policy frameworks to realize projected emissions reductions without unintended trade-offs.[7]Transportation
Electric Vehicle
An electric vehicle (EV) is a road vehicle powered primarily by one or more electric traction motors that draw energy from rechargeable electrochemical batteries or other onboard energy storage devices. Unlike internal combustion engine vehicles, EVs produce no tailpipe emissions during operation, though their total environmental impact depends on electricity generation sources and manufacturing processes.[11] Modern passenger EVs typically use lithium-ion batteries, which store energy chemically and enable ranges of 200–500 miles per charge, depending on model and conditions.[12] The first EVs emerged in the late 19th century, with practical models like William Morrison's 1890 battery-powered carriage achieving speeds up to 14 miles per hour.[3] By 1900, EVs accounted for about one-third of U.S. vehicles due to their quiet operation and reliability compared to early gasoline engines, but cheap oil, Henry Ford's Model T in 1908, and electric starter innovations shifted dominance to internal combustion by the 1920s.[3] Revived interest in the 1970s amid oil crises led to prototypes like GM's EV1 in 1996, but mass adoption accelerated post-2010 with Tesla's Roadster (2008) and Model S (2012), which demonstrated viable range and performance using advanced lithium-ion cells.[3] EV technology centers on high-voltage battery packs, typically 40–100 kWh for sedans, paired with permanent magnet or induction motors delivering instant torque and efficiencies over 90%, far exceeding gasoline engines' 20–30%.[12] Charging occurs via Level 1 (120V household outlets, 3–5 miles per hour added), Level 2 (240V, 20–60 miles per hour), or DC fast chargers (up to 350 kW, 100–200 miles in 30 minutes).[13] Regenerative braking recaptures energy, extending range by 10–20% in urban driving.[12] Global EV sales reached 17 million units in 2024, comprising 20% of new light-duty vehicle sales, driven by policy incentives, falling battery costs (down 89% since 2010 to under $140/kWh), and models from Tesla, BYD, and Volkswagen.[4] In the first half of 2025, sales exceeded 9 million, capturing 23% market share, with China leading at over 50% of global volume due to subsidies and domestic supply chains.[14] Projections for full-year 2025 indicate over 20 million sales, though growth slowed in North America to 6% year-over-year amid subsidy phase-outs and infrastructure limits.[15] Lifecycle greenhouse gas emissions for EVs are 50–70% lower than comparable gasoline vehicles in regions with cleaner grids, such as Europe, per IEA analyses accounting for battery production (which emits 40–70% more upfront CO2 than ICE manufacturing) and 150,000–200,000 miles of use.[16] [17] In coal-heavy grids like parts of India or Poland, breakeven may exceed 100,000 miles.[18] EPA data confirms U.S. EVs emit less CO2 equivalent over lifetimes, even including upstream grid emissions averaging 0.4 kg CO2/kWh nationally.[11] However, battery mineral extraction—lithium from brine evaporation in South America's "lithium triangle" (using 500,000 gallons of water per ton) and cobalt from Democratic Republic of Congo mines (where child labor affects 40,000 workers)—poses ecological risks including aquifer depletion and toxic runoff, though recycling rates are rising to 95% for lithium by 2030 targets.[19] [20] Advantages include lower fuel costs (electricity at $0.03–0.05 per mile vs. $0.10–0.15 for gasoline), minimal maintenance (no oil changes, fewer moving parts), and superior acceleration from torque curves.[13] Disadvantages encompass high purchase prices (20–50% above ICE equivalents before incentives), range degradation in cold weather (20–40% loss below freezing), and charging times averaging 8–10 hours for full home replenishment versus 5 minutes for refueling.[21] Public infrastructure remains uneven, with the U.S. at 170,000 stations in 2025 versus Europe's denser network, exacerbating "range anxiety" for long trips. Supply chain vulnerabilities, including 70% of refined cobalt from China, further challenge scalability.[22]Physics
Electronvolt
The electronvolt (symbol eV) is a unit of energy defined as the kinetic energy acquired by a single unbound electron when accelerated through an electric potential difference of one volt in vacuum.[23] Although not part of the International System of Units (SI), it is accepted for use alongside SI units due to its convenience in fields involving subatomic scales.[23] One electronvolt equals exactly 1.602176634 × 10^{-19} joules.[24] This unit arose in the context of early 20th-century measurements requiring knowledge of the elementary charge, following Robert Millikan's 1909 oil-drop experiment that determined the electron's charge.[25] It provides a practical scale for energies too small to express efficiently in joules; for example, atomic binding energies and photon energies in visible light range from a few eV to several eV, while nuclear reactions involve MeV scales.[26] In particle physics, the electronvolt expresses kinetic energies, rest masses (via E = mc²), and interaction strengths, with accelerator beam energies often in GeV or TeV. Common multiples include the kiloelectronvolt (keV = 10³ eV), megaelectronvolt (MeV = 10⁶ eV), gigaelectronvolt (GeV = 10⁹ eV), and teraelectronvolt (TeV = 10^{12} eV).[27] The unit's adoption stems from the natural coupling of electron charge and voltage in electrostatic phenomena, yielding energies directly measurable in experiments like photoelectric effect or mass spectrometry.[28]Mathematics and Statistics
Expected Value
In probability theory, the expected value of a random variable X, denoted E[X], represents the long-run average outcome of repeated independent trials of the random experiment associated with X.[29] This value is computed as a probability-weighted sum or integral over the possible outcomes, providing a measure of the central tendency under uncertainty.[30] For instance, the expected value of a fair six-sided die roll is 3.5, obtained by averaging the faces weighted equally at probability $1/6 each: E[X] = (1 + 2 + 3 + 4 + 5 + 6)/6 = 3.5.[29] For a discrete random variable taking values x_i with probabilities P(X = x_i), the expected value is E[X] = \sum_i x_i P(X = x_i), assuming the sum converges absolutely.[31] For a continuous random variable with probability density function f(x), it is E[X] = \int_{-\infty}^{\infty} x f(x) \, dx, provided the integral exists.[32] These definitions extend to functions of random variables, where E[g(X)] = \sum_i g(x_i) P(X = x_i) for discrete cases.[33] A key property is linearity of expectation: for random variables X and Y (possibly dependent) and constants a, b, E[aX + bY] = a E[X] + b E[Y].[34] This holds without requiring independence, as the proof follows from substituting the definitions: E[X + Y] = \sum (x_i + y_j) P(X=x_i, Y=y_j) = \sum x_i \sum_j P(X=x_i, Y=y_j) + \sum y_j \sum_i P(X=x_i, Y=y_j) = E[X] + E[Y].[35] Linearity simplifies computations in complex systems, such as estimating the expected number of fixed points in a random permutation via indicator variables.[36] Expected value also relates to variance via \operatorname{Var}(X) = E[X^2] - (E[X])^2, linking it to measures of spread.[33] In statistics, E[X] coincides with the population mean \mu for distributions like the normal or binomial.[37] Applications include risk assessment in finance, where negative expected returns signal unprofitable gambles under repeated play, and decision theory, prioritizing actions maximizing expected utility.[30] However, expected value alone does not capture risk or tail events, necessitating complementary metrics like variance or higher moments.[33]Finance and Economics
Enterprise Value
Enterprise value (EV), also known as total enterprise value (TEV), represents the theoretical price tag to acquire a company's entire operations, accounting for both equity and debt claims on its assets.[38] It is calculated by adding a firm's market capitalization to its total debt and subtracting cash and cash equivalents, as cash can theoretically offset acquisition costs while debt transfers to the buyer.[39] The standard formula is: EV = Market Capitalization + Total Debt − Cash and Cash Equivalents More comprehensive variants include adjustments for minority interest, preferred stock, and sometimes non-operating assets, yielding EV = Equity Value + Net Debt + Preferred Stock + Minority Interest.[40] Unlike market capitalization, which solely reflects the equity portion valued by shareholders via stock price multiplied by outstanding shares, EV provides a fuller picture of a company's value by incorporating its capital structure.[38] For instance, a firm with significant debt will have an EV exceeding its market cap, signaling higher acquisition costs, whereas excess cash reduces EV relative to market cap.[39] This distinction arises because market cap ignores debt obligations that an acquirer must assume, making EV preferable for cross-company comparisons, especially those with varying leverage.[40] EV is widely applied in mergers and acquisitions to estimate takeover prices and in relative valuation multiples, such as EV/EBITDA, which normalizes for capital structure differences and focuses on operational performance.[38] For example, in discounted cash flow analysis, EV aligns with the present value of free cash flows to the firm, excluding financing effects.[39] Practitioners note that miscalculations, like overlooking pension liabilities or using book debt values instead of market values, can distort EV, underscoring the need for market-based inputs where possible.[41]Photography
Exposure Value
In photography, exposure value (EV) is a dimensionless index that combines a lens's f-number and shutter speed to specify the exposure intensity required for a given scene luminance, normalized to an ISO arithmetic speed of 100.[42] It is a core element of the Additive System of Photographic Exposure (APEX), which uses base-2 logarithms for exposure parameters, enabling additive combinations where a change of 1 EV unit doubles or halves the light reaching the sensor or film.[42] This system simplifies comparisons across settings, as any aperture-shutter pair yielding the same EV delivers equivalent exposure under identical conditions, disregarding secondary effects like depth of field or motion blur.[43] The EV is derived from EV = Av + Tv, where Av (aperture value) equals 2 × log₂(f-number) and Tv (time value) equals -2 × log₂(exposure time in seconds).[42] This expands to the direct formula EV = log₂[(f-number)² / exposure time].[43] For example, f/8 at 1/60 second yields EV 12, matching f/4 at 1/240 second or f/16 at 1/15 second, all at ISO 100.[43] APEX originated in the early 1960s via American Standards Association documents like PH2.12-1961 for exposure meters, promoting logarithmic uniformity over arithmetic scales; while manual camera dials once featured EV scales for quick setting swaps, digital automation reduced visible use, though APEX encoding remains in EXIF metadata per ISO standards for digital still images.[42] EV is calibrated to scene luminance via EV = Bv + Sv, where Bv (brightness value) reflects subject luminance in candelas per square meter and Sv (speed value) is the film's logarithmic ISO equivalent (Sv = log₂(ISO/3.125) approximately for ISO 100 as Sv = 5).[42] It contrasts with light value (LV), a luminance-based measure independent of sensitivity; EV equals LV at ISO 100, but higher ISOs lower the required EV for the same LV by allowing less light.[44] For instance, full sunlight on a gray card (LV 15, approximately 88,000 lux) demands EV 15 at ISO 100 (e.g., 1/125 second at f/16), but EV 13 at ISO 400.[44] The following table illustrates equivalent exposures for selected EV levels at ISO 100:[43]| Shutter Speed | f/2.8 | f/4 | f/5.6 | f/8 | f/11 | f/16 |
|---|---|---|---|---|---|---|
| 1/125 s | 10 EV | 11 EV | 12 EV | 13 EV | 14 EV | 15 EV |
| 1/60 s | 9 EV | 10 EV | 11 EV | 12 EV | 13 EV | 14 EV |
| 1/30 s | 8 EV | 9 EV | 10 EV | 11 EV | 12 EV | 13 EV |
Project Management
Earned Value
Earned value (EV), also referred to as budgeted cost of work performed (BCWP), quantifies the approved budget associated with the work actually completed on a project at a given point in time. It serves as a key metric in earned value management (EVM), a methodology that objectively measures project performance by integrating scope, schedule, and cost data to forecast outcomes and identify variances early.[45][46] Unlike simple progress tracking, EV requires verifiable methods such as percentage completion based on objective criteria, milestones achieved, or units of work delivered, avoiding subjective estimates or arbitrary formulas.[47] EV is calculated by applying the project's performance measurement baseline (PMB)—the time-phased budget plan—to the actual work accomplished, ensuring alignment with the defined scope. For instance, if a task budgeted at $100,000 is 40% complete based on predefined metrics like inspected deliverables, its EV equals $40,000. This contrasts with planned value (PV, or budgeted cost of work scheduled, BCWS), which reflects the budgeted cost for work scheduled up to that point, and actual cost (AC, or actual cost of work performed, ACWP), which captures incurred expenditures regardless of progress.[45][48] EVM originated in the U.S. Department of Defense during the 1960s as part of efforts to enhance control over complex programs, evolving from earlier cost-schedule control systems and formalized in standards like the ANSI/EIA-748 guidelines.[48][46] EV enables derivation of variances and performance indices to assess efficiency:| Metric | Formula | Interpretation |
|---|---|---|
| Schedule Variance (SV) | EV - PV | Positive value indicates ahead of schedule; negative, behind schedule.[45] |
| Cost Variance (CV) | EV - AC | Positive value indicates under budget; negative, over budget.[45] |
| Schedule Performance Index (SPI) | EV / PV | Greater than 1: ahead of schedule; less than 1: behind; equal to 1: on schedule.[45] |
| Cost Performance Index (CPI) | EV / AC | Greater than 1: under budget; less than 1: over budget; equal to 1: on budget.[45] |