Solving Electrical Circuit Homework Questions

[kitkat794]

Homework Statement

i've been trying to do these but i keep getting different answers from back of book.

1)When there is a potential difference of 1.0 V between two points in an electrical ciruit, what is the mean amount of energy lost by an electron when moving between these two points? This amount of energy has a special name, the electronvolt, symbol eV.

2)When an electron is accelerated across a potential difference of about 15 V it has enough energy to ionise a nitrogen atom, that is, to remove an electron from the atom by collision with it. How many attojoule, aJ is this? 1.0aJ=1.0 x 10^-18 J.

3) The electrical circuit in a small torch consists of a battery of e.m.f 3.0 V and a bulb in series. The potential difference across the bulb is 2.7 V when the current in the bulb is 0.3 A.

a) Calcuate how much energy is converted in one minute:
i) from chemical form to electrica form in battery
ii) from electrical form to thermal energy and light in the bulb

Homework Equations

The Attempt at a Solution

1) ?
2) 1 volt= 1 joule per couloumb second so 15V = 15 joules percoloumb second. then i did 15 divided by 1x10^-18 and i got 1.5 x10^19 aJ which is wrong (should be 2.4aJ)

3)a) i know i meant to use the formula for electromotive force but i don't know how to work out the charge to put it in this (answer should be 54J)

ii) use formua for potential difference which again needs charge and i don't know how to work it out (answer should be 48.6 J)

 

[supratim1]

1. energy = charge * potential diff.

multiply charge of electron with 1V, that is 1 eV

 

[supratim1]

2. same case, energy is 15V*(charge of 1 electron), convert units.

 

[gneill]

For 3, do you know how to determine the power (rate of energy delivered or consumed) given voltage and current? Then, if you have the power, how can you find the total energy over a given time period?