1.'by/in contrast'和'on the contrary'

By contrast / In contrast

I often use these two phrases in both writing task 1 and 2. They are exactly the same, and are used in a similar way to "however" or "on the other hand" to introduce a contrast / comparison. Put "By / In contrast" at the beginning of a sentence, with a comma after "contrast".
我经常在短作文和长作文里使用这2个短语。他们的用法完全相同。和however、on the other hand相似,它们用于介绍相反的观点或进行比较。By/In contrast可以用于句首,后面要加逗号。

Example
例如:

Unemployment rose in the UK. By contrast, the number of unemployed people in Canada fell.

On the contrary

I've never used this phrase in any of my IELTS lessons. It doesn't mean the same thing as "by / in contrast". We use "on the contrary" to deny that something is true, and to explain that the opposite is true.
我从未在我的雅思课中用过这个短语。它和by / in contrast的意思不同。我们用on the contrary来否定某事,并解释与之相反的事是真实的。

Example
例如:

- Person 1: "You had some problems with your hotel, didn't you?"

- Person 2: "On the contrary, the hotel was great, but the airline lost my suitcase."

2. affect和effect

"Affect" is a verb. Don't write "affect on".
Affect是动词。不要用affect on。

Smoking affects your health. (smoking affects on your health)
The Internet is affecting our way of life.
Children are affected by what they see on television.

"Effect" is a noun. Do write "have an effect on".
Effect是名词。可以用have an effect on。

Smoking has a harmful effect on your health.
The Internet is having a significant effect on our way of life.
Television can have a negative effect on children.