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# Radiographic Physics

### Johnston, 1st Ed., Chapter 4

Ohm's Law: an electric circuit contains 20 amps and 6 ohms. What is the voltage? | V = IR V = 20 x 6 V = 120 |

Ohm's Law: an electric circuit contains 100 volts and 15 amps. What is the resistance? | V = IR R = V/I R = 100/15 R = 6.7 ohms |

If a series circuit contains 3 elements each with 20 amps and 1.5 ohms, 2.5 ohms, and 2 ohms respectively, how many volts are contained in each element, and how many total volts are in the circuit? | 20 x 1.5 = 30 volts; 20 x 2.5 = 50 volts; 20 x 2 = 40 volts 30 + 50 + 40 = 120 volts "Voltages are added in series circuits" |

If a series circuit contains 120 volts, 20 amps, and has 3 elements with 1.5 ohms, 2.5 ohms, and 2 ohms respectively, what is the total current on each element? | I (t) = I (1) = I (2) = I (3) Since the total current in the circuit = the current on each element, the total current is 20 amps and each element = 20 amps "Current remains constant in series circuits" |

If a series circuit contains 120 volts, 20 amps, and 3 elements with 1.5 ohms, 2.5 ohms, and 2 ohms respectively, what is the total resistance in the circuit? | R (t) = R (1) + R (2) + R (3)....... Total resistance equals the sum of resistances on each element. So, 1.5 + 2.5+ 2 = 6 ohms "Resistance is additive in series circuits" |

A parallel circuit has 3 elements containing 8 ohms, 12 ohms, and 15 ohms. If the circuit contains 110 volts, what is the total voltage on each element? | V (t) = V (1) = V (2) = V (3)..... The total voltage of a parallel circuit is equal to the voltage in each element of the circuit. Total voltage = 110 Each element contains 110 volts "voltage remains constant in parallel circuits" |

A parallel circuit has 3 elements containing 8 ohms, 12 ohms, and 15 ohms. If the circuit contains 110 volts, what is the total resistance? | 1/R (t) = 1/R (1) + 1/R (2) + 1/R (3) 1/R (t) = 1/8 + 1/12 + 1/15 15/120 + 10/120 + 8/120 = 33/120 R (t) = 120/33 = 3.6 ohms "Resistance in a parallel circuit is the sum of the inverse resistance values" |

A transformer contains 1000 turns on its primary side and 200,000 turns on its secondary side. What is the turns ratio for this transformer? | N (s)/N (p) 200,000/1000 200/1 or 200:1 "Direct relationship" |

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