Please help someone Charge and current questions nightmare

In summary: The number of electrons on the beam at any instant is 1.0x10 p9. 2. The beam current in a television tube is 32 mA. 3. The speed of light is 3.0 · 1010 cm/sec. 4. It takes a single electron about 4.2 · 10−7 sec to travel 21 cm. 5. The current of electrons in the beam is given as I = 32 mA. 6. The number of electrons that pass a specific point in one second is given by 1.0x10 p14.
  • #1
Emilia.watson
2
0
Please help someone! Charge and current questions! nightmare!

Hi! I'm new here and joined this forum for any future help :) So i just started Physics A level and i have the worst teacher ever who is so unhelpful... :( I don't know what to do... He set us 2 questions for homework and it looks nothing like what we did in class... I even asked for help in the end of the lesson and he didn't even get it himself!

Someone please help me... I have tried but i end up with funny answers that don't look very convincing :(

Help would be appreciated... Could someone please write down the method and why? THANK-YOU SO MUCH! really...couldn't be anymore grateful Emilia x

The beam current in a television tube is 32mA.The electrons travel at a speed of 4.2x10₁₇ through distance of 21cm. (sorry about the powers...they seem to be below..)
1. Number of electrons striking the screen in 1 hour is : ( p stands for power..by the way )
a)2.0x10 p 17
b)7.2x10 p 20
c)1.2x10 p22
d)7.2x10 p23

1b) The number of electrons on the beam at any instant
a)1.0x10 p9
b)1.0x10 p11
c)1.0x10 p12
d)1.0x10 p14


2. State what physical quantity is represented by each term in the equation:

I=NAvq

b) A semiconducting strip 6.0mm wide and 0.5mm thick carries a current of 10mA.

If the value of n for the semiconducting material is 7.0x10 p22m₋₃, show that the drift speed of the charge carriers, which carry a charge of 1.6x10 p -19 C, is about 0.3ms₋₁.

c) The drift speed for electrons in a copper strip of the same dimensions and carrying the same current would be about 10 p -7₇ ms₋₁
. Use the equation to explain why this value is very different from that of the semiconductor.

Thank you so much everyone. I really don’t want anyone to get the wrong impression of me being lazy and not doing it. Because I do find it very hard... and I have tried as much of it as i could... Also just...this Physics teacher...he’s urgh! I wouldn’t be asking if have i known what to do... maybe just to see if i did it right... but... I really would like some help. Thank-you again! Emilia x
 
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  • #2


Emilia.watson said:
The beam current in a television tube is 32mA.The electrons travel at a speed of 4.2x10₁₇ through distance of 21cm.

You will need to clarify this part for a start. The speed of light is 3.0 · 1010 cm/sec, so the electrons cannot be moving faster than that. Is the numerical value you've shown typed correctly and is it in cm/sec?
 
  • #3


Hi there :) I know right! It says 4.2x10 to the power of 7 ms-1 in the textbook. i don't get it ...:(
 
  • #4


Emilia.watson said:
The beam current in a television tube is 32mA.The electrons travel at a speed of 4.2x10₁₇ through distance of 21cm. (sorry about the powers...they seem to be below..)
1. Number of electrons striking the screen in 1 hour is : ( p stands for power..by the way )
a)2.0x10 p 17
b)7.2x10 p 20
c)1.2x10 p22
d)7.2x10 p23

1b) The number of electrons on the beam at any instant
a)1.0x10 p9
b)1.0x10 p11
c)1.0x10 p12
d)1.0x10 p14

Let's start with this problem. So the speed of the electron's is v = 4.2 · 107 m/sec or 4.2 · 109 cm/sec . How long does it take a single electron to travel the 21 cm. from the emitter to the screen?

Also, the current of electrons in the beam is given as I = 32 mA . How much charge is flowing in the beam past a specific location each second? (Remember that Amperes are Coulombs per second.) How many electrons does this mean are passing that point in one second?
 
  • #5


Hi Emilia! I'm sorry to hear that you're struggling with your physics homework and your teacher. It can be frustrating when the material seems difficult and your teacher isn't providing much help. Don't worry, we're here to help!

First, let's take a look at the questions you were given. For the first question, we need to find the number of electrons striking the screen in one hour. We can do this by using the formula:

Q = I x t

Where Q is the charge (in coulombs), I is the current (in amperes), and t is the time (in seconds). In this case, we are given the current as 32mA, but we need to convert it to amperes by dividing by 1000. So our current is 0.032A. We also need to convert the time to seconds, so one hour is 3600 seconds. Plugging these values into the formula, we get:

Q = 0.032A x 3600s = 115.2C

This is the total charge that passes through the screen in one hour. To find the number of electrons, we need to divide this value by the charge of one electron, which is 1.6x10^-19C. So the number of electrons is:

115.2C / 1.6x10^-19C = 7.2x10^23 electrons

Therefore, the correct answer is d) 7.2x10p23.

For the second question, we need to find the number of electrons in the beam at any instant. To do this, we need to use the formula:

Q = n x V x A x t

Where Q is the charge (in coulombs), n is the number of electrons per unit volume (in m^-3), V is the volume (in m^3), A is the cross-sectional area (in m^2), and t is the time (in seconds). We are given the current as 32mA, but we need to convert it to amperes by dividing by 1000. So our current is 0.032A. We also need to convert the distance to meters, so 21cm is 0.21m. Plugging these values into the formula, we get:

Q = n x 0.21m x A x t

We don't know the
 

What is the difference between charge and current?

Charge refers to the amount of electrically charged particles, known as electrons, in a material or object. Current, on the other hand, refers to the movement of these charged particles. In other words, charge is the potential for an electric current to flow, while current is the actual flow of the charged particles.

How do I calculate the amount of current in a circuit?

To calculate the current in a circuit, you can use Ohm's law, which states that current (I) is equal to the voltage (V) divided by the resistance (R). In mathematical terms, this can be written as I=V/R. You can also use a multimeter to directly measure the current in a circuit.

Why is it important to properly charge electronic devices?

Properly charging electronic devices is important because it ensures that they function correctly and efficiently. Overcharging or undercharging can lead to damage to the device's battery, which can affect its performance and lifespan. It is also important to use the correct charger for a device, as using a different charger can result in excessive current and potentially damage the device.

What happens if there is too much current in a circuit?

If there is too much current in a circuit, it can cause overheating and potentially damage the components in the circuit. This can lead to malfunctions or even electrical fires. It is important to use the appropriate circuit protection, such as fuses or circuit breakers, to prevent excessive current from damaging the circuit.

How can I protect myself from electric shock while working with circuits?

To protect yourself from electric shock while working with circuits, it is important to always turn off the power source before handling any wires or components. You should also wear protective gear, such as gloves and goggles, and make sure to use insulated tools. It is also recommended to work on a dry surface and to avoid working alone in case of an accident.

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