Riddles about school

I am small. I am often white. You can take away your pencil marks with me.

I am on the wall. I am dark. I am usually black or green. You can write on me with chalk.

I need electricity. I have a screen. I can send email. You can play games on me.

I am long. I am made of plastic or wood. You can use me for drawing straight lines. You can measure things with me

I have a ball shape. I have one leg to stand on. I have the map of the world. I am very useful on Geography lesson.

I am small. I am an electronic instrument. I can add, subtract, multiply and divide. You can use me on Maths lesson