Batteries

• How Much Does a Smartphone Battery’s Mass Increase When Charged?
  A charged smartphone battery is slightly heavier: estimate the change from its stored energy using Δm = ΔE/c², typically well below a nanogram.
• How to Measure the EMF of a Cell
  Measure a cell’s EMF with a high-resistance voltmeter for a quick estimate or a potentiometer for a null-balance measurement.
• How Does Electrical Grounding Work?
  Electrical ground can set a circuit's voltage reference or protect against faults. Learn how current returns to its source and when earth matters.
• How Does a Cell’s Internal Resistance Vary With Temperature?
  A cell’s internal resistance usually falls as temperature rises because its electrolyte conducts better, but the trend depends on chemistry and conditions.
• Does Current Run Forever in Water?
  Current can continue through water while a complete circuit and electrode reactions are sustained, but real cells eventually change or run out of reactants.
• Can You Store AC in a Battery?
  Batteries store energy chemically, not AC or DC current. Learn why they charge with DC and how converters let AC power charge them.
• What Happens When Different Batteries Are Connected in Parallel?
  Different-voltage batteries in parallel can drive current into each other. Learn how to estimate that current and why mismatched batteries can be unsafe.
• What Happens Atomically When Batteries Are Connected in Series?
  In a series connection, each battery’s chemical reactions contribute energy per unit charge, so aligned emfs add to give a larger total voltage.