Transcript Ohm’s Law
Ohm’s Law PSSA Requirement Unit 9 Honors Physics A look at electricity • • • • Static Electricity Charges are stationary (mostly) Look at force between charges Electric field around charged particles Potential from a charged particle Current Electricity • Charges are moving (flowing) • Look at how circuits work • Resistance to the flow A New Language • Quantities – Current (unit - Amperes (A) – Voltage (unit - Volt (V)) – Resistance (unit - Ohms (Ω)) • Option - Z gives Ω Symbol Electric Current Q I t Current is defined as the rate at which charge flows past a given point Unit of Current: A (ampere) = C / s Current and Flow • Either positive or negative particles can flow • Conventional Current - direction positive charge would flow Microscopic View of Current Circuit Requirements • Circuit - complete path of conductors for electrons (closed loop) • Battery - Power Source - pushes electrons around • Something to use the current - light bulb • Switch Circuits Measuring Current and Voltage • Ammeter - measures current – Must be placed in series (in line) with object it is measuring • Voltmeter - measures potential difference between two points in a circuit – Must be placed in parallel (around) the object it is measuring • Multimeter - Can measure more than 1 quantity Voltage and Current • When a voltage is applied to a conductor current is proportional to the applied voltage • Proportionality Constant is called Resistance I V V IR Resistance / Ohm’s Law V R I Units - Ω (ohms) Ohm’s Law Notes • Georg Simon Ohm (1787 - 1854) studied electrical resistance • ∆V = I R • ∆V is the potential drop across the resistor • Ohm’s Law is only valid for certain materials - ohmic materials Ohmic and Non-Ohmic Materials Ohm’s Law Problems An iron carries a current of 6.4 A when connected to a 120 V source. What is the resistance of the steam iron?