Featured contributor PhD Applied Physics; former research associate at a national metrology lab.

Dr. Helena Ortiz

Senior Reviewer, Science & Engineering

0 calculators 0 articles Member since Jun 2026

About

Helena is the senior technical reviewer for physics, chemistry, and unit-conversion calculators. She is the last pair of eyes on every formula — checking constants, units, and edge cases against primary sources and standards bodies.

She holds a PhD in Applied Physics and previously held a research post at a national metrology lab.

Areas of expertise

Physics Chemistry Unit conversion Measurement standards

Education & credentials

BSc Physics — Universidad Complutense de Madrid
PhD Applied Physics — Stanford University

Chemistry

Extended Debye-Hückel Ionic Activity Calculator

Calculates the mean ionic activity coefficient γ using the extended Debye-Hückel equation from ionic strength, charge, a...

basic

5,836 4.0 1 min

Physics / Electricity

Capacitor Charge from Capacitance and Voltage Calculator

Compute the electric charge stored on a parallel-plate (or any) capacitor from its capacitance and the voltage across it...

basic

13,325 3.9 1 min

Physics / Electricity

Isolated Sphere Capacitance from Radius Calculator

Compute the self-capacitance of an isolated conducting sphere of radius R (relative to a virtual ground at infinity): C...

basic

6,728 4.4 1 min

Physics

Light Travel Time Calculator

Compute the time for light (c = 299 792 458 m/s) to traverse a given distance, with results in seconds, minutes, hours,...

basic

21,724 3.9 1 min

Chemistry

Radioactive Decay Activity Calculator

Calculates radioactive activity at any elapsed time from initial activity and decay constant or half-life. Returns activ...

basic

9,070 4.2 1 min

Physics / Electricity

Parallel-Plate Capacitance Calculator

Compute the capacitance of a parallel-plate capacitor from the plate area A, the separation d, and the dielectric consta...

basic

2,798 4.9 1 min

Everyday Life

Lawn Fertilizer Application Rate Calculator

Calculates how much fertilizer (bags or kg) to apply to a lawn based on lawn area, recommended nitrogen rate, and fertil...

basic

23,109 4.0 1 min

Physics

Malus's Law Polarization Calculator

Compute the transmitted intensity of linearly polarized light through a polarizer using Malus's law I = I₀ · cos²(θ), wh...

basic

22,454 4.2 1 min

Physics / Electricity

Quality Factor Q of an RLC Resonant Circuit Calculator

Compute the quality factor Q of a series RLC circuit at resonance: Q = ω₀·L / R, where ω₀ = 1/√(LC). High Q (sharp reson...

basic

14,544 4.8 1 min

Statistics

Bootstrap Standard Error & Resampling Calculator

Estimates standard error from a sample using the bootstrap approximation from sample standard deviation and sample size.

basic

1,996 4.7 1 min

Everyday Life

Fence Post and Rail Materials Calculator

Calculates number of fence posts = ceil(total length / spacing) + 1, rails = posts × rails_per_span, and boards if a pan...

basic

17,511 4.1 1 min

Chemistry / Solutions

Colligative Properties Combined Osmotic Boiling Freezing Calculator

Calculates three colligative properties of an aqueous solution: osmotic pressure (π), boiling point elevation (ΔTb), and...

basic

4,998 4.2 1 min

Showing 361 to 372 of 504 results

No articles published yet.

Reviewed by Dr. Helena Ortiz

These calculators were technically reviewed by Dr. Helena Ortiz for accuracy.

Chemistry / Reactions

Equilibrium Constant Calculator

Compute the equilibrium constant K_c from the concentrations of two products (with stoichiometric coefficients 1) divide...

basic

5,060 4.0 1 min

Conversions / Length

Length Converter

Convert between meters, kilometers, miles, feet, inches, and yards.

Featured basic

4,964 4.2 1 min

Chemistry / Solutions

Combined Gas Law Calculator

Find the missing pressure, volume, or temperature using the combined gas law for a fixed amount of gas.

basic

5,360 4.2 1 min

Physics / Electricity

Capacitance Calculator

Compute the capacitance of a parallel-plate capacitor from plate area, plate separation, and the dielectric constant.

basic

12,524 4.1 1 min

Chemistry / Solutions

pOH Calculator

Compute pOH from hydroxide ion concentration and the matching pH at 25 °C.

basic

18,221 4.2 1 min

Ecology / Carbon Footprint

Carbon Footprint Calculator

Estimate your annual personal CO₂e footprint from home energy, driving, flying, and diet — with adjustable emission fact...

Featured basic

15,825 4.9 1 min

Calcify

Browse categories

Dr. Helena Ortiz

Extended Debye-Hückel Ionic Activity Calculator

Capacitor Charge from Capacitance and Voltage Calculator

Isolated Sphere Capacitance from Radius Calculator

Light Travel Time Calculator

Radioactive Decay Activity Calculator

Parallel-Plate Capacitance Calculator

Lawn Fertilizer Application Rate Calculator

Malus's Law Polarization Calculator

Quality Factor Q of an RLC Resonant Circuit Calculator

Bootstrap Standard Error & Resampling Calculator

Fence Post and Rail Materials Calculator

Colligative Properties Combined Osmotic Boiling Freezing Calculator

Reviewed by Dr. Helena Ortiz

Equilibrium Constant Calculator

Length Converter

Combined Gas Law Calculator

Capacitance Calculator

pOH Calculator

Carbon Footprint Calculator